UPSTREAM: udp: fix behavior of wrong checksums

(cherry pick from commit a3cfde2a)

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
Change-Id: Ia396f80a0fe2eaca4d2ee1cdcb45ad14f5e2b927
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit:0d12967a5f5ea9cd10e224f0dafbf90d46c06bd9
Git-repo: https://android.googlesource.com/kernel/msm


Signed-off-by: Yogendra Charya Tangalapally <yogendra@codeaurora.org>