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/Makefile.am b/openbsc/include/openbsc/Makefile.am
index d9d8e99..2b54c43 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -13,6 +13,7 @@
 	bss.h \
 	bts_ipaccess_nanobts_omlattr.h \
 	chan_alloc.h \
+	common_bsc.h \
 	common_cs.h \
 	crc24.h \
 	ctrl.h \