[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/include/linux/skbuff.h b/include/linux/skbuff.h
index fd4e12f..94e4991 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -994,7 +994,7 @@
  *
  *	Return the number of bytes of free space at the head of an &sk_buff.
  */
-static inline int skb_headroom(const struct sk_buff *skb)
+static inline unsigned int skb_headroom(const struct sk_buff *skb)
 {
 	return skb->data - skb->head;
 }
@@ -1347,7 +1347,7 @@
  *	Returns true if modifying the header part of the cloned buffer
  *	does not requires the data to be copied.
  */
-static inline int skb_clone_writable(struct sk_buff *skb, int len)
+static inline int skb_clone_writable(struct sk_buff *skb, unsigned int len)
 {
 	return !skb_header_cloned(skb) &&
 	       skb_headroom(skb) + len <= skb->hdr_len;