Revert "sock_diag: allow concurrent operations"

This reverts commit 161d4fc0 which is
commit 1d55a697 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: If6ddd015afec0f53b849679c83570f05fb17e57b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>