res_pjsip_pubsub: Check supported headers for eventlist when subscribing to
resource list

https://wiki.asterisk.org/wiki/display/AST/Resource+List+Subscription+Test+Plan
According to the off-nominal plan, if evenlist support is not specified in a
SUBSCRIBE's supported header(s), that subscription should be rejected with an
error.

ASTERISK-23871
Reported by: Mark Michelson
Review: https://reviewboard.asterisk.org/r/3960/diff/#index_header
........

Merged revisions 422836 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@422837 f38db490-d61c-443f-a65b-d21fe96a405b