net: Make setsockopt() optlen be unsigned.

This provides safety against negative optlen at the type
level instead of depending upon (sometimes non-trivial)
checks against this sprinkled all over the the place, in
each and every implementation.

Based upon work done by Arjan van de Ven and feedback
from Linus Torvalds.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c
index f1118d9..66c7a20 100644
--- a/net/ipx/af_ipx.c
+++ b/net/ipx/af_ipx.c
@@ -1292,7 +1292,7 @@
  * socket object. */
 
 static int ipx_setsockopt(struct socket *sock, int level, int optname,
-			  char __user *optval, int optlen)
+			  char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	int opt;