Send re-register packets by GRQ (gatekeeper request) interval

(close issue ASTERISK-20094)

Patches:
   ASTERISK-20094-2.patch 
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Merged revisions 371060 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 371061 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371081 65c4cc65-6c06-0410-ace0-fbb531ad65f3