Changes

Move include sigtran/m2ua_types.h -> sigtran/protocol/m2ua.h

That file contains only protocol (over-the-wire) related values, similar
to already existing sigtran/protocol/m3ua.h.
Hence, move it where it should be.
This is fine since there's no user of such a header, it's only used
internally by m2ua_test.

Change-Id: I66d8a335bbd1c55edab8a120d85e6aee1922433c