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/decnet/af_decnet.c b/net/decnet/af_decnet.c
index 77d4028..7a58c87 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -157,7 +157,7 @@
 static struct hlist_head dn_wild_sk;
 static atomic_t decnet_memory_allocated;
 
-static int __dn_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen, int flags);
+static int __dn_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen, int flags);
 static int __dn_getsockopt(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen, int flags);
 
 static struct hlist_head *dn_find_list(struct sock *sk)
@@ -1325,7 +1325,7 @@
 	return err;
 }
 
-static int dn_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen)
+static int dn_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	int err;
@@ -1337,7 +1337,7 @@
 	return err;
 }
 
-static int __dn_setsockopt(struct socket *sock, int level,int optname, char __user *optval, int optlen, int flags)
+static int __dn_setsockopt(struct socket *sock, int level,int optname, char __user *optval, unsigned int optlen, int flags)
 {
 	struct	sock *sk = sock->sk;
 	struct dn_scp *scp = DN_SK(sk);