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>

include/net/sctp/structs.h

@@ -544,7 +544,7 @@ struct sctp_af {
 					 int level,
 					 int optname,
 					 char __user *optval,
-					 int optlen);
+					 unsigned int optlen);
 	int		(*getsockopt)	(struct sock *sk,
 					 int level,
 					 int optname,
@@ -554,7 +554,7 @@ struct sctp_af {
 					 int level,
 					 int optname,
 					 char __user *optval,
-					 int optlen);
+					 unsigned int optlen);
 	int		(*compat_getsockopt)	(struct sock *sk,
 					 int level,
 					 int optname,