Introduce libosmo-gprs-sm

This patch itnroduces all the boilerplate required to build and package
a new libosmo-gprs-sm.so library, which aims to contain the SM layer
implementation.
A minimal implementation is provided together with a unit test,
showcasing Activation of a PDP Context and requesting implicit GPRS
attach to GMM if it is not yet attached.
This commit also adds/improves code in GMM layer implementing the GMMSM
SAP which is used to interact SM<->GMM.

Related: OS#5501
Change-Id: I9b4a9a6364f7799540475e7e1d10ab2310768281
---
M Makefile.am
M configure.ac
M contrib/libosmo-gprs.spec.in
M debian/control
A debian/libosmo-gprs-sm-dev.install
A debian/libosmo-gprs-sm0.install
M include/osmocom/gprs/Makefile.am
M include/osmocom/gprs/gmm/gmm_ms_fsm.h
M include/osmocom/gprs/gmm/gmm_prim.h
M include/osmocom/gprs/gmm/gmm_private.h
A include/osmocom/gprs/sm/Makefile.am
A include/osmocom/gprs/sm/sm.h
A include/osmocom/gprs/sm/sm_ms_fsm.h
A include/osmocom/gprs/sm/sm_pdu.h
A include/osmocom/gprs/sm/sm_prim.h
A include/osmocom/gprs/sm/sm_private.h
A libosmo-gprs-sm.pc.in
M src/Makefile.am
M src/gmm/gmm.c
M src/gmm/gmm_ms_fsm.c
M src/gmm/gmm_prim.c
A src/sm/Makefile.am
A src/sm/misc.c
A src/sm/sm.c
A src/sm/sm_ms_fsm.c
A src/sm/sm_pdu.c
A src/sm/sm_prim.c
M tests/Makefile.am
M tests/gmm/gmm_prim_test.c
M tests/gmm/gmm_prim_test.err
M tests/gmm/gmm_prim_test.ok
A tests/sm/Makefile.am
A tests/sm/sm_prim_test.c
A tests/sm/sm_prim_test.err
A tests/sm/sm_prim_test.ok
M tests/testsuite.at
36 files changed, 2,453 insertions(+), 60 deletions(-)