[pedantic] Declare abis_nm_bs11_reset_resource to avoid a warning in bsc_hack.c

This command is BS11 specific and was put in the appropriate section
of the header file.

diff --git a/include/openbsc/abis_nm.h b/include/openbsc/abis_nm.h
index d153415..63a568a 100644
--- a/include/openbsc/abis_nm.h
+++ b/include/openbsc/abis_nm.h
@@ -383,6 +383,7 @@
 int abis_nm_software_load(struct gsm_bts *bts, const char *fname, u_int8_t win);
 
 /* Siemens / BS-11 specific */
+int abis_nm_bs11_reset_resource(struct gsm_bts *bts);
 int abis_nm_bs11_db_transmission(struct gsm_bts *bts, int begin);
 int abis_nm_bs11_create_object(struct gsm_bts *bts, enum abis_bs11_objtype type,
 			  u_int8_t idx, u_int8_t attr_len, const u_int8_t *attr);