This patch adds a new attribute to msgb objects. This new
attribute will store a pointer to the routing information,
in the case of the A-bis link, this will be used to store
e1inp_sign_link instead of struct gsm_bts_trx.
This deprecates msg->trx, that can be removed once all
application are ported to use msg->dst.
This patch moves all GSM-specific definitions to include/osmocom/gsm.
Moreover, the headers in include/osmocore/ have been moved to
include/osmocom/core.
This has been proposed by Harald Welte and Sylvain Munaunt.
Tested with `make distcheck'.
Signed-off-by: Pablo Neira Ayuso <pablo@gnumonks.org>