PJSIP_MEDIA_OFFER: override configuration on refresh

When using the PSJIP_MEDIA_OFFER dialplan function it was not
overriding an endpoint's configured codecs on refresh unless
they had a shared codec between the two.

This patch makes it so whatever is set using PJSIP_MEDIA_OFFER
is used when creating the SDP for a refresh no matter what.

ASTERISK-28878 #close

Change-Id: I0f7dc86fd0fb607c308e6f98ede303c54d1eacb6