res/res_pjsip_sdp_rtp: Fix leak of local ICE candidates when applying to SDP

When an SDP is created for an outgoing request/response, the ICE candidates
obtained from the RTP instance are currently leaked. This causes the ao2
container that holds the candidates to never properly be reclaimed when the
RTP instance is destroyed.

This patch properly decrements the ICE candidates' container if it is
successfully obtained.

ASTERISK-24769 #close
Reported by: Matt Jordan
........

Merged revisions 431600 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@431601 65c4cc65-6c06-0410-ace0-fbb531ad65f3