Revert "tcp: deny tcp_disconnect() when threads are waiting"

This reverts commit 0377416c which is
commit 4faeee0cf8a5d88d63cdbc3bab124fb0e6aed08c upstream.

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

Bug: 161946584
Change-Id: I80e8272468138b5144f9780b6ea5f8d107988e2a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>