Intersect codec sets for local_merge strategy, REF 16784

Here is our pjsip_endpoint.conf:
outgoing_call_offer_pref = local_merge
incoming_call_offer_pref = remote_first

For outgoing calls we use local_merge (UNION) which means "Merge the lists with the preferred
codecs first"
For incomming calls we use remote_first (INTERSECT) which means "Only common codecs with the
preferred codecs first"

When UPDATE was received for incoming call, device responded with
488 Not Acceptable Here with Reason:Q.850;cause=16
When UPDATE was received for outgoing call, device responded with
488 Not Acceptable Here with Reason:Q.850;cause=58 
BYE
 
After this commit we have the same behaviour for UPDATE during both incoming and outgoing call.

Incoming calls were fixed in similar way before in fb501964.