merge from codename-pineapple and astobj2 47499:

simplify __sip_ack() removing a strcmp for looking up packets.

no functional change, only performance, so don't need to merging
to earlier branches now.

Approved By: oej



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47538 65c4cc65-6c06-0410-ace0-fbb531ad65f3