VTY: backwards compatibility for 'logging level sms'

when the SMS code was moved into libosmocore, its logging prefix was
changed from 'sms' to 'lsms', which breaks existing config files.

This introduces a deprecated/hidden vty command to make sure those
config files are still parsed OK, and will simply print a warning
message about the config needing some update.
diff --git a/openbsc/src/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 60eacad..441ee1e 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -911,6 +911,18 @@
 	return CMD_SUCCESS;
 }
 
+/* this is just for backwards compatibility as the sms code moved into
+ * libosmocore and old config files no longer parse... */
+DEFUN_DEPRECATED(log_level_sms, log_level_sms_cmd,
+	"logging level sms (everything|debug|info|notice|error|fatal)",
+	".HIDDEN")
+{
+	vty_out(vty, "%% 'logging level sms' is now called 'logging level "
+		"lsms', please update your config %s", VTY_NEWLINE);
+
+	return CMD_SUCCESS;
+}
+
 int bsc_vty_init_extra(void)
 {
 	osmo_signal_register_handler(SS_SCALL, scall_cbfn, NULL);
@@ -952,5 +964,7 @@
 	install_element(MNCC_INT_NODE, &mnccint_def_codec_f_cmd);
 	install_element(MNCC_INT_NODE, &mnccint_def_codec_h_cmd);
 
+	install_element(CFG_LOG_NODE, &log_level_sms_cmd);
+
 	return 0;
 }