udp: Fix rcv socket locking

udp: Fix rcv socket locking

[ Upstream commits d97106ea52aa57e63ff40d04479016836bbb5a4e and
   93821778def10ec1e69aa3ac10adee975dad4ff3 ]

The previous patch in response to the recursive locking on IPsec
reception is broken as it tries to drop the BH socket lock while in
user context.

This patch fixes it by shrinking the section protected by the
socket lock to sock_queue_rcv_skb only.  The only reason we added
the lock is for the accounting which happens in that function.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>