sip_to_pjsip: Set correct tls transport method

A recent update had a copy/paste error where the unused variable 'val' was
being passed to the set_value function instead of the 'method' value itself.

This patch passes in the right variable.

ASTERISK-22374

Change-Id: I895b7b3779ce4442bc58b8ec40d59dd29bb43f06