res_pjsip: Fix contact authenticate_qualify endpoint lookup when qualifing a contact.

* Fixed bad use of ao2_find() in on_endpoint().

* Replaced use of find_endpoints() with find_an_endpoint() since only the
first found endpoint is ever needed.

* Fixed qualify_contact_cb() to update the contact with the aor
authenticate_qualify setting.  Otherwise, permanent contacts in the aor
type sections would have a config line order dependancy.

* Fixed off nominal path contact ref leak in qualify_contact().  The
comment saying the unref is not needed was wrong.

* Fixed off nominal path use of the endpoint parameter if it is NULL in
send_out_of_dialog_request().

* Added missing off nominal path unref of pjsip tdata in
send_out_of_dialog_request().

* Fixed off nominal path failing to call the callback in send_request_cb()
when the request is challenged for authentication.

* Eliminated silly RAII_VAR() use in qualify_contact_cb().

* Updated ast_sip_send_request() doxygen to better reflect reality.

(closes issue ASTERISK-23254)
Reported by: rmudgett

Review: https://reviewboard.asterisk.org/r/3381/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@411141 f38db490-d61c-443f-a65b-d21fe96a405b