res_pjsip_session.c: Send 100 Trying out earlier to prevent retransmissions.

res_pjsip_session.c: Send 100 Trying out earlier to prevent retransmissions.

If ICE is enabled and a STUN server does not respond then we will block
until we give up on the STUN response.  This will take nine seconds.  In
the mean time the peer that sent the INVITE will send retransmissions.

* Restructure res_pjsip_session.c:new_invite() to send a 100 Trying out
earlier to prevent these retransmissions.

ASTERISK-26890

Change-Id: Ie3fc611e53a0eff6586ad55e4aacad81cf6319a8