gbproxy: Refactor gb_proxy.c into several files

This patch moves several functions and declarations out of gb_proxy.c
to make them reusable by other components and to separate them by
context and task.

Counter enums (prefix is changed to gbproxy_):
  enum gbprox_global_ctr -> gprs/gb_proxy.h
  enum gbprox_peer_ctr -> gprs/gb_proxy.h

Generic Gb parsing (prefix is changed to gprs_gb_):
  struct gbproxy_parse_context -> openbsc/gprs_gb_parse.h
  gbprox_parse_dtap() -> gprs/gprs_gb_parse.c
  gbprox_parse_llc() -> gprs/gprs_gb_parse.c
  gbprox_parse_bssgp() -> gprs/gprs_gb_parse.c
  gbprox_log_parse_context() -> gprs/gprs_gb_parse.c
  *_shift(), *_match() -> gprs/gprs_gb_parse.c (no prefix)
  gbprox_parse_gmm_* -> gprs/gprs_gb_parse.c (static)
  gbprox_parse_gsm_* -> gprs/gprs_gb_parse.c (static)

MI testing/parsing (prefix gprs_ added):
  is_mi_tmsi() -> gprs/gprs_utils.c
  is_mi_imsi() -> gprs/gprs_utils.c
  parse_mi_tmsi() -> gprs/gprs_utils.c

TLLI state handling (prefix is changed to gbproxy_):
  gbprox_*tlli* -> gprs/gb_proxy_tlli.c
  (except gbprox_patch_tlli, gbproxy_make_sgsn_tlli)

Message patching (prefix is changed to gbproxy_):
  gbprox_*patch* -> gprs/gb_proxy_patch.c
  gbprox_check_imsi -> gprs/gb_proxy_patch.c

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index bad38c8..4d0c9cd 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -14,7 +14,8 @@
 endif
 
 osmo_gbproxy_SOURCES =  gb_proxy.c gb_proxy_main.c gb_proxy_vty.c \
-			gprs_llc_parse.c crc24.c gprs_utils.c
+			gb_proxy_patch.c gb_proxy_tlli.c \
+			gprs_gb_parse.c gprs_llc_parse.c crc24.c gprs_utils.c
 osmo_gbproxy_LDADD = 	$(top_builddir)/src/libcommon/libcommon.a \
 			$(OSMO_LIBS)