TT#29926 NGCP refreshes the session even if STT is not supported

Unset Sems internal Session Timers in case B leg doesn't support it
(no Timer in Supported header of 200OK message).

Change-Id: I21fd1de2a088ab71042cbee54bd00cd1ea9f5a0b

debian/patches/series

@@ -28,3 +28,4 @@ build-system-revamp.patch
 fix-build-with-newer-openssl.patch
 sipwise/0020-TT-9521-fix-200OK-without-SPD.patch
 sipwise/usage-reporting.patch
+sipwise/session_timers

debian/patches/sipwise/session_timers

@@ -0,0 +1,25 @@
+--- a/core/plug-in/session_timer/SessionTimer.cpp
++++ b/core/plug-in/session_timer/SessionTimer.cpp
+@@ -346,7 +346,21 @@ void SessionTimer::updateTimer(AmSession
+   if (((reply.code < 200) || (reply.code >= 300)) &&
+       (!(accept_501_reply && reply.code == 501)))
+     return;
+-  
++
++  // verify if B leg supports Session Timers
++  remote_timer_aware =
++      key_in_list(getHeader(reply.hdrs, SIP_HDR_SUPPORTED, SIP_HDR_SUPPORTED_COMPACT),
++                  TIMER_OPTION_TAG);
++
++  if (!remote_timer_aware) {
++    // timer NOT supported by B leg
++    DBG("Session Timer NOT supported by leg B, removing internal session timer intervals");
++    session_timer_conf.setEnableSessionTimer("no");
++    removeTimers(s);
++    return;
++  }
++
++  // timer supported by B leg
+   // determine session interval
+   string sess_expires_hdr = getHeader(reply.hdrs, SIP_HDR_SESSION_EXPIRES,
+ 				      SIP_HDR_SESSION_EXPIRES_COMPACT, true);