bsc/vty: Add 'no bsc-welcome-text' command

There was no command to reset a bsc-welcome-text string, so it has
been added.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_vty.c b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
index 501d9f5..8eaa55b 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_vty.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
@@ -111,8 +111,11 @@
 	vty_out(vty, " ip.access rtp-base %d%s", msc->rtp_base, VTY_NEWLINE);
 	vty_out(vty, " timeout-ping %d%s", msc->ping_timeout, VTY_NEWLINE);
 	vty_out(vty, " timeout-pong %d%s", msc->pong_timeout, VTY_NEWLINE);
+
 	if (msc->ussd_welcome_txt)
 		vty_out(vty, " bsc-welcome-text %s%s", msc->ussd_welcome_txt, VTY_NEWLINE);
+	else
+		vty_out(vty, " no bsc-welcome-text%s", VTY_NEWLINE);
 
 	if (msc->ussd_msc_lost_txt && msc->ussd_msc_lost_txt[0])
 		vty_out(vty, " bsc-msc-lost-text %s%s", msc->ussd_msc_lost_txt, VTY_NEWLINE);
@@ -361,7 +364,7 @@
 DEFUN(cfg_net_msc_welcome_ussd,
       cfg_net_msc_welcome_ussd_cmd,
       "bsc-welcome-text .TEXT",
-      "Set the USSD notification to be sent.\n" "Text to be sent\n")
+      "Set the USSD notification to be sent\n" "Text to be sent\n")
 {
 	struct osmo_msc_data *data = osmo_msc_data(vty);
 	char *str = argv_concat(argv, argc, 0);
@@ -373,6 +376,19 @@
 	return CMD_SUCCESS;
 }
 
+DEFUN(cfg_net_msc_no_welcome_ussd,
+      cfg_net_msc_no_welcome_ussd_cmd,
+      "no bsc-welcome-text",
+      NO_STR "Clear the USSD notification to be sent\n")
+{
+	struct osmo_msc_data *data = osmo_msc_data(vty);
+
+	talloc_free(data->ussd_welcome_txt);
+	data->ussd_welcome_txt = 0;
+
+	return CMD_SUCCESS;
+}
+
 DEFUN(cfg_net_msc_lost_ussd,
       cfg_net_msc_lost_ussd_cmd,
       "bsc-msc-lost-text .TEXT",
@@ -612,6 +628,7 @@
 	install_element(MSC_NODE, &cfg_net_msc_ping_time_cmd);
 	install_element(MSC_NODE, &cfg_net_msc_pong_time_cmd);
 	install_element(MSC_NODE, &cfg_net_msc_welcome_ussd_cmd);
+	install_element(MSC_NODE, &cfg_net_msc_no_welcome_ussd_cmd);
 	install_element(MSC_NODE, &cfg_net_msc_lost_ussd_cmd);
 	install_element(MSC_NODE, &cfg_net_msc_no_lost_ussd_cmd);
 	install_element(MSC_NODE, &cfg_net_msc_type_cmd);