move to libcommon-cs: net init 2: move bsc_network_init decl to new .h

bsc_network_init() is more fit to live in a BSC specific header, move it to new
common_bsc.h. It will probably also absorb the BSC-specific part of gsm_network
in the future.

Adjust header includes across the board. Particularly, fix abis_nm.h by
explicitly including gsm_data.h: it so far relied on other headers to do that,
which now is no longer always given.

Change-Id: I9edfb1e748bb1cb484fadd48b0406f5b3098e89b
diff --git a/openbsc/include/openbsc/abis_nm.h b/openbsc/include/openbsc/abis_nm.h
index 965f158..2465452 100644
--- a/openbsc/include/openbsc/abis_nm.h
+++ b/openbsc/include/openbsc/abis_nm.h
@@ -26,6 +26,8 @@
 #include <osmocom/gsm/abis_nm.h>
 #include <osmocom/gsm/protocol/gsm_12_21.h>
 
+#include <openbsc/gsm_data.h>
+
 struct cell_global_id {
 	uint16_t mcc;
 	uint16_t mnc;