Include the Username field in SIP Registry events when Status is registered

In ASTERISK-17888, the AMI Registry event during SIP registrations was supposed
to include the Username field. Somehow, one of the events was missed. This
patch corrects that - the Username field should be included in all AMI Registry
events involving SIP registrations.

(issue ASTERISK-17888)

(closes issue ASTERISK-21201)
Reported by: Dmitriy Serov
patches:
  chan_sip.c.diff uploaded by Dmitriy Serov (license 6479)
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Merged revisions 382847 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 382848 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@382852 f38db490-d61c-443f-a65b-d21fe96a405b