netfilter: bitwise: fix reduce comparisons

The `nft_bitwise_reduce` and `nft_bitwise_fast_reduce` functions should
compare the bitwise operation in `expr` with the tracked operation
associated with the destination register of `expr`.  However, instead of
being called on `expr` and `track->regs[priv->dreg].selector`,
`nft_expr_priv` is called on `expr` twice, so both reduce functions
return true even when the operations differ.

Fixes: be5650f8

 ("netfilter: nft_bitwise: track register operations")
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>