### Description

I'm using dispatcher module like:

``` loadmodule "dispatcher.so" modparam("dispatcher", "list_file", "/etc/kamailio/dispatcher.list") modparam("dispatcher", "ds_probing_mode", 1) modparam("dispatcher", "ds_ping_interval", 60) ``` With records like: ``` 1 sip:sip.host.com;transport=tls 0 1 socket=tls:111.222.233.10:5061;ping_from=sip:my-domain-01.com 2 sip:sip.host.com;transport=tls 0 1 socket=tls:111.222.233.20:5061;ping_from=sip:my-domain-02.com ```

In event_route[tm:local-request] I'm modifying 'Contact' and would like to specify what client TLS profile to use via server name or server id. ``` event_route[tm:local-request] { if(is_method("OPTIONS")) { append_hf("Contact: sip:some-host.com;transport=tls\r\n"); $xavp(tls=>server_name)=$fd; $xavp(tls[0]=>server_id)=$fd; } } ``` Setting 'tls' xavp doesn't make any difference and default client TLS profile is being used.

It happens because in src/modules/tm/uac.c there is a code: ``` t_run_local_req() ... tm_xdata_swap(new_cell, &backup_xd, 0); ... /* restore original environment */ tm_xdata_swap(new_cell, &backup_xd, 1); ``` which resets any xavp changes done in event_route[tm:local-request].

Expected behaviour: ability to use xavp in tm:local-request route. That would allow to choose TLS client profile for dispatcher initiated requests.

### Possible Solutions

As a hack, in tm_xdata_swap() for mode=1, don't restore xavp list if it was NULL. ``` if (x->xavps_list != NULL && *x->xavps_list==NULL) { // .... don't restore empty list... } else { xavp_set_list(x->xavps_list); } ``` This change allows to select required TLS profile for dispatcher requests.

### Additional Information

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

``` version: kamailio 5.3.5 (x86_64/linux) ff2f8c-dirty flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: ff2f8c -dirty compiled on 10:19:05 Jul 28 2020 with gcc 7.5.0 ```

* **Operating System**:

``` Linux xx 4.15.0-111-generic #112-Ubuntu SMP Thu Jul 9 20:32:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux ```