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

sigtran: xua_msg.h,msg_types.h: Make headers private

Those headers are only used internally in libosmo-sigtran, since those
objects have no real use outside of it. Mark the headers as no-install,
which implicitly makes them private.

Only API osmo_xua_msg_tall_ctx_init() is used by osmo-bsc, hence why
it's left in the existing public header.

This decreases the amount of public APIs the libosmo-sigtran has.

Change-Id: Icd23bf9c9364c33ea2ba709e3ef4439813a168f4

sigtran: Make osmo_ss7_route_table APIs private

The routing table is actually handled internally through VTY and no user
is making use of it.
Make it private, to ease extension in the future (it will be extended
to eg. support  combined link load sharing).

Change-Id: Ie7c709c9849ef3d50aef94f79751c9c4a010c92a

sigtran: Add API osmo_ss7_route_get_dest_as()

This is needed by users willing to get the AS from a routing entry, i.e.
osmo-bsc needs to access this information in order to inject MGCP into
the IPA multiplex conn transporting the SCCPLite signalling.

Change-Id: Ife63bd384d247a761e0b89505ea71c41a4a16d9b