Be more consistent with the return code for requests received from invalid domain.

Be more consistent with the return code for requests received from invalid domain.

When Asterisk receives an INVITE from an external domain when allowexternaldomains=no
send a 403 instead of a 404. This is consistent with Asterisk's behavior when receiving
a REGISTER in this situation.

(Closes issue ASTERISK-19601)
Reported by Matthew Jordan
Patches:
	ASTERISK-19601-no401.patch uploaded by Mark Michelson (License #5049)
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Merged revisions 369302 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 369303 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@369304 65c4cc65-6c06-0410-ace0-fbb531ad65f3