sip_to_pjsip: Write media_encryption.

When using the migration script sip_to_pjsip.py, encryption=yes got missing and
media_encryption=sdes was not written to pjsip.conf, because of a typo.

ASTERISK-22374

Change-Id: I0fc3e55dc512a57603ae0fef41baacccf2a35c05