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/drivers/atm/fore200e.c b/drivers/atm/fore200e.c
index 10f000d..f766cc4 100644
--- a/drivers/atm/fore200e.c
+++ b/drivers/atm/fore200e.c
@@ -1795,7 +1795,7 @@
 
 
 static int
-fore200e_setsockopt(struct atm_vcc* vcc, int level, int optname, void __user *optval, int optlen)
+fore200e_setsockopt(struct atm_vcc* vcc, int level, int optname, void __user *optval, unsigned int optlen)
 {
     /* struct fore200e* fore200e = FORE200E_DEV(vcc->dev); */