bsc: Allow to generate new system information online

Increase the bcch_change_mark and generate a new copy of the
system information. Make the method public, add a small test
case. Manually verified using the FakeBTS. I don't know if
the MS will re-read these SIs.

Related: SYS#739
diff --git a/openbsc/src/libbsc/bsc_init.c b/openbsc/src/libbsc/bsc_init.c
index 796d027..a59ab3d 100644
--- a/openbsc/src/libbsc/bsc_init.c
+++ b/openbsc/src/libbsc/bsc_init.c
@@ -121,7 +121,7 @@
 }
 
 /* set all system information types */
-static int set_system_infos(struct gsm_bts_trx *trx)
+int gsm_bts_trx_set_system_infos(struct gsm_bts_trx *trx)
 {
 	int i, rc;
 	struct gsm_bts *bts = trx->bts;
@@ -269,7 +269,7 @@
 		rsl_nokia_si_begin(trx);
 	}
 
-	set_system_infos(trx);
+	gsm_bts_trx_set_system_infos(trx);
 
 	if (trx->bts->type == GSM_BTS_TYPE_NOKIA_SITE) {
 		/* channel unspecific, power reduction in 2 dB steps */