bsc: Get rid of module param mp_media_mgw_offer_ipv6

This param is not needed anymore sincenew releases used in -latest don't
need to disable it.
Let's keep the possibility to change behavior from within test and leave
v6 enabled by default as it used to be.

Related: OS#5042
Change-Id: Ic693885dd3d4259dc6ce80643d25c7d432148d3d
1 file changed