define mncc_recv_cb_t to avoid code dup

Put mncc_recv_cb_t in common_cs.h to avoid header include complications: if placing
right above struct gsm_network, one must include gsm_data.h to use
mncc_recv_cb_t as function parameter in a header, which will include
gsm_data_shared.h, which will include common_cs.h (future knowledge). Since I will
need to use mncc_recv_cb_t in common_cs.h, including gsm_data.h from there would
introduce an #include loop. Avoid that and define mncc_recv_cb_t in common_cs.h to
begin with.

Change-Id: I2e64cffa563750ce9f3172ffba6f9cf5b9280e9c
diff --git a/openbsc/src/libbsc/net_init.c b/openbsc/src/libbsc/net_init.c
index 57e3599..da13a52 100644
--- a/openbsc/src/libbsc/net_init.c
+++ b/openbsc/src/libbsc/net_init.c
@@ -26,7 +26,7 @@
 struct gsm_network *gsm_network_init(void *ctx,
 				     uint16_t country_code,
 				     uint16_t network_code,
-				     int (*mncc_recv)(struct gsm_network *, struct msgb *))
+				     mncc_recv_cb_t mncc_recv)
 {
 	struct gsm_network *net;
 	const char *default_regexp = ".*";