skb: make drop reason booleanable

We have a number of cases where function returns drop/no drop
decision as a boolean. Now that we want to report the reason
code as well we have to pass extra output arguments.

We can make the reason code evaluate correctly as bool.

I believe we're good to reorder the reasons as they are
reported to user space as strings.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -314,6 +314,7 @@ struct sk_buff;
  * used to translate the reason to string.
  */
 enum skb_drop_reason {
+	SKB_NOT_DROPPED_YET = 0,
 	SKB_DROP_REASON_NOT_SPECIFIED,	/* drop reason is not specified */
 	SKB_DROP_REASON_NO_SOCKET,	/* socket not found */
 	SKB_DROP_REASON_PKT_TOO_SMALL,	/* packet size is too small */