IAX2: refactor nativebridge transfer

remove triple checking of iaxs[fr->callno]->transferring

reduce indentation.

Reported by: alecdavis
Tested by: alecdavis
alecdavis (license 585)

Review https://reviewboard.asterisk.org/r/2602/
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Merged revisions 391065 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@391084 f38db490-d61c-443f-a65b-d21fe96a405b
fix bad edit after conflict resolution
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Merged revisions 391107 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@391111 f38db490-d61c-443f-a65b-d21fe96a405b