osmo-hnbgw lacks support for an co-located media gateway. This makes it
virtually impossible to isolate the HNB from the core network properly.
Lets add MGCP support to osmo-hnbgw so that it can control a co-located
media gateway to relay the RTP streams between HNB and core network.
Change-Id: Ib9b62e0145184b91c56ce5d8870760bfa49cc5a4
Related: OS#5152