[TIPC]: Remove redundant NULL check when discarding buffers

This patch eliminates a null pointer check when discarding a
TIPC message buffer, since kfree_skb() already handles this
situation.

Acknowledgements to Florian Westphal (fw@strlen.de> for
suggesting this enhancement.
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/core.h

@@ -334,7 +334,6 @@ static inline struct sk_buff *buf_acquire(u32 size)
 
 static inline void buf_discard(struct sk_buff *skb)
 {
-	if (likely(skb != NULL))
 	kfree_skb(skb);
 }