netlink_linearize: use u64 conversion for 64bit quantities

netlink_linearize: use u64 conversion for 64bit quantities

nft generated two 4-byte swaps for conntrack byte/packet counters,
which are 64bit host-endian values:

byteorder reg 1 = hton(reg 1, 4, 8) ]

This makes the kernel perform two htonl() calls, but we need
a cpu_to_be64 conversion instead (reg 1, 8, 8).

Without this a rule like 'ct original packets > 10'
matched when counter was between 1 and 10.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>