move MGW endpoint FSM from osmo-bsc to here

Move mgw_endpoint_fsm from osmo-bsc here as osmo_mgcpc_ep_fsm. Apply various
renames for consistency. Use osmo_tdef from libosmocore instead of osmo-bsc's
(so far) local T_defs API.

Change T23042 to T2427001, which is a slightly less arbitrary number and
slightly more extendable in the future (2427 corresponds to the default MGCP
port at osmo-mgw, 001 is the first MGCP timer and so far the only one).

Change-Id: I9a3effd38e72841529df6c135c077116981dea36
6 files changed