[NET]: Treat the sign of the result of skb_headroom() consistently

In some places, the result of skb_headroom() is compared to an unsigned
integer, and in others, the result is compared to a signed integer.  Make
the comparisons consistent and correct.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9288220..3dbbb44 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3909,7 +3909,7 @@
 
 	while (before(start, end)) {
 		struct sk_buff *nskb;
-		int header = skb_headroom(skb);
+		unsigned int header = skb_headroom(skb);
 		int copy = SKB_MAX_ORDER(header, 0);
 
 		/* Too big header? This can happen with IPv6. */