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>

drivers/atm/eni.c

@@ -2031,7 +2031,7 @@ static int eni_getsockopt(struct atm_vcc *vcc,int level,int optname,
 
 
 static int eni_setsockopt(struct atm_vcc *vcc,int level,int optname,
-    void __user *optval,int optlen)
+    void __user *optval,unsigned int optlen)
 {
 	return -EINVAL;
 }