net: Introduce sk_tx_queue_mapping

Introduce sk_tx_queue_mapping; and functions that set, test and
get this value. Reset sk_tx_queue_mapping to -1 whenever the dst
cache is set/reset, and in socket alloc. Setting txq to -1 and
using valid txq=<0 to n-1> allows the tx path to use the value
of sk_tx_queue_mapping directly instead of subtracting 1 on every
tx.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/sock.c b/net/core/sock.c
index 38713aa..934d967 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -357,6 +357,7 @@
 	struct dst_entry *dst = sk->sk_dst_cache;
 
 	if (dst && dst->obsolete && dst->ops->check(dst, cookie) == NULL) {
+		sk_tx_queue_clear(sk);
 		sk->sk_dst_cache = NULL;
 		dst_release(dst);
 		return NULL;
@@ -953,7 +954,8 @@
 	void *sptr = nsk->sk_security;
 #endif
 	BUILD_BUG_ON(offsetof(struct sock, sk_copy_start) !=
-		     sizeof(osk->sk_node) + sizeof(osk->sk_refcnt));
+		     sizeof(osk->sk_node) + sizeof(osk->sk_refcnt) +
+		     sizeof(osk->sk_tx_queue_mapping));
 	memcpy(&nsk->sk_copy_start, &osk->sk_copy_start,
 	       osk->sk_prot->obj_size - offsetof(struct sock, sk_copy_start));
 #ifdef CONFIG_SECURITY_NETWORK
@@ -997,6 +999,7 @@
 
 		if (!try_module_get(prot->owner))
 			goto out_free_sec;
+		sk_tx_queue_clear(sk);
 	}
 
 	return sk;