src: use namespace prefix osmo_signal*

Summary of changes:

s/signal_cbfn/osmo_signal_cbfn/g
s/register_signal_handler/osmo_signal_register_handler/g
s/unregister_signal_handler/osmo_signal_unregister_handler/g
s/dispatch_signal/osmo_signal_dispatch/g
diff --git a/openbsc/src/libbsc/abis_rsl.c b/openbsc/src/libbsc/abis_rsl.c
index 941a4ba..4d61dc0 100644
--- a/openbsc/src/libbsc/abis_rsl.c
+++ b/openbsc/src/libbsc/abis_rsl.c
@@ -55,7 +55,7 @@
 	struct lchan_signal_data sig;
 	sig.lchan = lchan;
 	sig.mr = resp;
-	dispatch_signal(SS_LCHAN, sig_no, &sig);
+	osmo_signal_dispatch(SS_LCHAN, sig_no, &sig);
 }
 
 static uint8_t mdisc_by_msgtype(uint8_t msg_type)
@@ -1806,7 +1806,7 @@
 
 	ipac_parse_rtp(lchan, &tv);
 
-	dispatch_signal(SS_ABISIP, S_ABISIP_CRCX_ACK, msg->lchan);
+	osmo_signal_dispatch(SS_ABISIP, S_ABISIP_CRCX_ACK, msg->lchan);
 
 	return 0;
 }
@@ -1823,7 +1823,7 @@
 
 	rsl_tlv_parse(&tv, dh->data, msgb_l2len(msg)-sizeof(*dh));
 	ipac_parse_rtp(lchan, &tv);
-	dispatch_signal(SS_ABISIP, S_ABISIP_MDCX_ACK, msg->lchan);
+	osmo_signal_dispatch(SS_ABISIP, S_ABISIP_MDCX_ACK, msg->lchan);
 
 	return 0;
 }
@@ -1839,7 +1839,7 @@
 		print_rsl_cause(LOGL_DEBUG, TLVP_VAL(&tv, RSL_IE_CAUSE),
 				TLVP_LEN(&tv, RSL_IE_CAUSE));
 
-	dispatch_signal(SS_ABISIP, S_ABISIP_DLCX_IND, msg->lchan);
+	osmo_signal_dispatch(SS_ABISIP, S_ABISIP_DLCX_IND, msg->lchan);
 
 	return 0;
 }