UPSTREAM: udp: fix behavior of wrong checksums

We have two problems in UDP stack related to bogus checksums :

1) We return -EAGAIN to application even if receive queue is not empty.
   This breaks applications using edge trigger epoll()

2) Under UDP flood, we can loop forever without yielding to other
   processes, potentially hanging the host, especially on non SMP.

This patch is an attempt to make things better.

We might in the future add extra support for rt applications
wanting to better control time spent doing a recv() in a hostile
environment. For example we could validate checksums before queuing
packets in socket receive queue.

Bug:29507402

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit beb39db5)

Bug: 31554728
Change-Id: I0096f0660d8951184f3a3b49a78702924f766cea
Tracked-On: https://jira01.devtools.intel.com/browse/AW-1795


Signed-off-by: Victor Tasayco Loarte <victorx.tasayco.loarte@intel.com>