net: shell: ping: correct argument count for net ping command

Since `<host>` is a mandatory argument, the (_mand, _opt) values
should be adjusted to 2 and 12, respectively.
Note that `_mand` includes the number of mandatory arguments,
including the command name (`ping` itself).

Signed-off-by: Pisit Sawangvonganan <pisit@ndrsolution.com>

subsys/net/lib/shell/ping.c

@@ -497,4 +497,4 @@ SHELL_STATIC_SUBCMD_SET_CREATE(net_cmd_ping,
 
 SHELL_SUBCMD_ADD((net), ping, &net_cmd_ping,
 		 "Ping a network host.",
-		 cmd_net_ping, 1, 13);
+		 cmd_net_ping, 2, 12);