Audit ast_sockaddr_resolve() usage for memory leaks.

Audit ast_sockaddr_resolve() usage for memory leaks.

Valgrind found some memory leaks associated with ast_sockaddr_resolve().
Most of the leaks had already been fixed by earlier memory leak hunt
patches.  This patch performs an audit of ast_sockaddr_resolve() and found
one more.

* Fix ast_sockaddr_resolve() memory leak in
apps/app_externalivr.c:app_exec().

* Made main/netsock2.c:ast_sockaddr_resolve() always set the addrs
parameter for safety so the pointer will never be uninitialized on return.
The same goes for res/res_pjsip_acl.c:extract_contact_addr().

Review: https://reviewboard.asterisk.org/r/4509/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@433056 65c4cc65-6c06-0410-ace0-fbb531ad65f3