net: core: drop null test before destroy functions

Remove unneeded NULL test.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@ expression x; @@
-if (x != NULL) {
\(kmem_cache_destroy\|mempool_destroy\|dma_pool_destroy\)(x);
x = NULL;
-}
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/sock.c

···
 		return;
 	kfree(rsk_prot->slab_name);
 	rsk_prot->slab_name = NULL;
-	if (rsk_prot->slab) {
-		kmem_cache_destroy(rsk_prot->slab);
-		rsk_prot->slab = NULL;
-	}
+	kmem_cache_destroy(rsk_prot->slab);
+	rsk_prot->slab = NULL;
 }
 
 static int req_prot_init(const struct proto *prot)
···
 	list_del(&prot->node);
 	mutex_unlock(&proto_list_mutex);
 
-	if (prot->slab != NULL) {
-		kmem_cache_destroy(prot->slab);
-		prot->slab = NULL;
-	}
+	kmem_cache_destroy(prot->slab);
+	prot->slab = NULL;
 
 	req_prot_cleanup(prot->rsk_prot);