misc: abis_nm.c Use the result of ret.

Use LOGP(DNM, LOGL_ERROR, ...); for errors in the
abis_nm_rx_sw_act_req method.

GCC warning:
abis_nm.c: In function ‘abis_nm_rx_sw_act_req’:
abis_nm.c:412:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]
diff --git a/openbsc/src/libbsc/abis_nm.c b/openbsc/src/libbsc/abis_nm.c
index a01826b..6568b53 100644
--- a/openbsc/src/libbsc/abis_nm.c
+++ b/openbsc/src/libbsc/abis_nm.c
@@ -422,12 +422,18 @@
 				      foh->obj_inst.trx_nr,
 				      foh->obj_inst.ts_nr, 0,
 				      foh->data, oh->length-sizeof(*foh));
+	if (ret != 0) {
+		LOGP(DNM, LOGL_ERROR,
+			"Sending SW ActReq ACK failed: %d\n", ret);
+		return ret;
+	}
 
 	abis_nm_tlv_parse(&tp, sign_link->trx->bts, foh->data, oh->length-sizeof(*foh));
 	sw_config = TLVP_VAL(&tp, NM_ATT_SW_CONFIG);
 	sw_config_len = TLVP_LEN(&tp, NM_ATT_SW_CONFIG);
 	if (!TLVP_PRESENT(&tp, NM_ATT_SW_CONFIG)) {
-		DEBUGP(DNM, "SW config not found! Can't continue.\n");
+		LOGP(DNM, LOGL_ERROR,
+			"SW config not found! Can't continue.\n");
 		return -EINVAL;
 	} else {
 		DEBUGP(DNM, "Found SW config: %s\n", osmo_hexdump(sw_config, sw_config_len));