bsc: Let the VTY verify that the timeout is a number

Before the old code allowed to specify "timeout-ping bla" which
would be parsed as '0' which would trigger a flood of pings. Use
the VTY code to parse it as a number.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_vty.c b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
index b1d09f3..ed4b05e 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_vty.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
@@ -357,7 +357,7 @@
 
 DEFUN(cfg_net_msc_ping_time,
       cfg_net_msc_ping_time_cmd,
-      "timeout-ping NR",
+      "timeout-ping <1-2147483647>",
       "Set the PING interval, negative for not sending PING\n"
       "Timeout in seconds\n")
 {
@@ -368,7 +368,7 @@
 
 DEFUN(cfg_net_msc_pong_time,
       cfg_net_msc_pong_time_cmd,
-      "timeout-pong NR",
+      "timeout-pong <1-2147483647>",
       "Set the time to wait for a PONG\n" "Timeout in seconds\n")
 {
 	struct osmo_msc_data *data = osmo_msc_data(vty);