When using the migration script sip_to_pjsip.py, both tos_sip and cos_sip got
missed, because of a typo. Therefore, cos and tos were not written to
pjsip.conf. Furthermore, that revealed a misuse of an internal function, caused
by a copy-and-paste error.

ASTERISK-22374

Change-Id: Id245ebadf70ab9776eb280c026288540af3af5c2