### Description
Kamailio with TOPOS enabled acts as a proxy between SIP client and SBC. When client sends "180 Ringing" without Contact header - kamailio does not forward it to SBC. If Contact header exists in "180 Ringing" - all works as expected.
### Troubleshooting
#### Reproduction
Load and configure topos module Make call with "180 Ringing" without Contact header - kamailio will not forward it.
#### Log Messages
``` ERROR: topos [tps_storage.c:340]: tps_storage_link_msg(): bad sip message or missing Contact hdr ```
#### SIP Traffic
``` SIP/2.0 180 Ringing Via: SIP/2.0/TLS 1.2.3.4:5061;branch=z9hG4bKef45.8c75f0bae8a59dfaec6ff533ff0f3b2d.0 From: sip:1111@1.2.3.4:5061;tag=02000879948559 To: sip:2.2.2.2@5.6.7.8:5061;transport=tls;user=phone;tag=SDbsq8499-y2pMOVV Call-ID: apdW7374315131g0bcGhEfDjFof CSeq: 988207425 INVITE User-Agent: agent Supported: replaces, outbound Content-Length: 0 ```
### Additional Information
* **Kamailio Version** - output of `kamailio -v`
``` version: kamailio 5.1.6 (x86_64/linux) flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, 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 ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144, MAX_LISTEN 16, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select ```
* **Operating System**:
``` Red Hat Enterprise Linux Server 7.3
3.10.0-514.el7.x86_64 #1 SMP Wed Oct 19 11:24:13 EDT 2016 x86_64 x86_64 x86_64 GNU/Linux ```