Closed #1677: Contact uses source port in initial registration.



git-svn-id: http://svn.pjsip.org/repos/pjproject@4888 74dad513-b988-da41-8d7b-12977e46ad98
More re #1677:
 - renamed the option to contact_use_src_port
 - added the missing pjsua2 API implementation


git-svn-id: http://svn.pjsip.org/repos/pjproject@4889 74dad513-b988-da41-8d7b-12977e46ad98