Don't override peer context with domain context.

(closes issue #17040)
Reported by: pprindeville
Patches:
      asterisk-1.6-bugid17040.patch uploaded by pprindeville (license 347)
Tested by: pprindeville

Review: https://reviewboard.asterisk.org/r/565/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@259957 65c4cc65-6c06-0410-ace0-fbb531ad65f3