[IPVS]: Make sure ip_vs_ftp ports are valid: module_param_array approach

I'm not entirely sure what happens in the case of a valid port,
at best it'll be silently ignored. This patch ensures that
the port values are unsigned short values, and thus always valid.

This is a second take at fixing this problem, it is simpler
and arguably more correct than the previous approach
that was committed as 3f5af5b353ca36aca4f8a46e3da2172f669dbbbc.
Prior to this patch a patch that reverses
3f5af5b353ca36aca4f8a46e3da2172f669dbbbc was sent.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipvs/ip_vs_ftp.c

@@ -44,8 +44,8 @@
  * List of ports (up to IP_VS_APP_MAX_PORTS) to be handled by helper
  * First port is set to the default port.
  */
-static int ports[IP_VS_APP_MAX_PORTS] = {21, 0};
-module_param_array(ports, int, NULL, 0);
+static unsigned short ports[IP_VS_APP_MAX_PORTS] = {21, 0};
+module_param_array(ports, ushort, NULL, 0);
 MODULE_PARM_DESC(ports, "Ports to monitor for FTP control commands");