Revert "bpf, sockmap: Improved check for empty queue"

This reverts commit ab5b5e32 which is
commit 405df89d 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: I867fcd33c08bd80f712bec954996ac28e263d779
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>