[NETFILTER]: nfnetlink_queue: deobfuscate entry lookups

A queue entry lookup currently looks like this:

find_dequeue_entry -> __find_dequeue_entry ->
	__find_entry -> cmpfn -> id_cmp

Use simple open-coded list walking and kill the cmpfn for
find_dequeue_entry. Instead add it to nfqnl_flush (after
similar cleanups) and use nfqnl_flush for both complete
flushes and flushing entries related to a device.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>