[sr-dev] [kamailio/kamailio] Branch ordering behavior changed since v5.3.4 (#2449)

[Cindy Leung]

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### Description

I'm appending two contacts / branches upon receiving a call.  This is a snippet of the config I'm using to debug:
```
        xlog ("=== branch 0: $(branch(uri)[0]), $(branch(q)[0])\n");
        xlog ("=== branch 1: $(branch(uri)[1]), $(branch(q)[1])\n");
        revert_uri();
        t_load_contacts();
        while (t_next_contacts()) {
            xlog ("==== $ru\n");
        }
```
We expect that the branches are rearranged by weight.  When t_next_contacts() is called, the $ru is being rewritten with the branch having the highest q value.  This behavior changed after upgrading to v5.4.0.  The order of the branches is now being reversed.

### Troubleshooting

#### Reproduction

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#### Debugging Data

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```
(paste your debugging data here)
```

#### Log Messages

In v5.4.0, this is what we're seeing in the logs
```
ERROR: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: === branch 0: sip:1001 at gateway2.carrierB.com;transport=udp, 200
ERROR: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: === branch 1: sip:1001 at gateway1.carrierB.com;transport=tcp, 300
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: tm [t_serial.c:526]: t_load_contacts(): load_contact mode not selected, using: 0
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: tm [t_serial.c:340]: ki_t_load_contacts_mode(): nr_branches is 2
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: <core> [core/xavp.c:539]: xavp_destroy_list(): destroying xavp list 0x7fcbe3103e20
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: tm [t_serial.c:890]: ki_t_next_contacts(): Appending branch uri-'sip:1001 at gateway1.carrierB.com;transport=tcp' dst-'' path-'' inst-'' ruid-'' location_ua-''
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: <core> [core/xavp.c:539]: xavp_destroy_list(): destroying xavp list 0x7fcbe3103b68
ERROR: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: ==== sip:1001 at carrierB
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: <core> [core/xavp.c:539]: xavp_destroy_list(): destroying xavp list 0x7fcbe3103890
ERROR: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: ==== sip:1001 at gateway2.carrierB.com;transport=udp
DEBUG: IBG_LOG: sipp-ci1-20200819163846-1-22 at 172.18.1.21: tm [t_serial.c:627]: ki_t_next_contacts(): no contacts in contacts_avp - we are done!
```

This was the behavior in v.5.3.4
```
ERROR: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: === branch 0: sip:1001 at gateway2.carrierB.com;transport=udp, 200
ERROR: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: === branch 1: sip:1001 at gateway1.carrierB.com;transport=tcp, 300
DEBUG: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: tm [t_serial.c:191]: ki_t_load_contacts(): nr_branches is 2
DEBUG: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: <core> [core/xavp.c:529]: xavp_destroy_list(): destroying xavp list 0x7f55bdf0c1d8
ERROR: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: ==== sip:1001 at gateway1.carrierB.com;transport=tcp
DEBUG: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: <core> [core/xavp.c:529]: xavp_destroy_list(): destroying xavp list 0x7f55bdf0bf00
ERROR: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: ==== sip:1001 at gateway2.carrierB.com;transport=udp
DEBUG: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: <core> [core/xavp.c:529]: xavp_destroy_list(): destroying xavp list 0x7f55bdf0bc28
ERROR: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: ==== sip:1001 at carrierB
DEBUG: IBG_LOG: sipp-ci1-20200819172941-1-22 at 172.18.1.21: tm [t_serial.c:460]: ki_t_next_contacts(): no contacts in contacts_avp - we are done!
```

#### SIP Traffic

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```
(paste your sip traffic here)
```

### Possible Solutions

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### Additional Information

  * **Kamailio Version** - output of `kamailio -v`

```
(paste your output here)
```

* **Operating System**:

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```
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```


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