netlink: Correct initial value of bytes counter in nftables rule

netlink: Correct initial value of bytes counter in nftables rule

Packages can be accounted by nftables through such command.
% nft add rule filter output ip daddr 8.8.8.8 counter

You can also give the initial values of packets and bytes.
% nft add rule filter output ip daddr 8.8.8.8 counter  packets 10 bytes 20

But packets and bytes are both initialized to 10 in above command for there is
a mistake in the program.

Signed-off-by: Yanchuan Nian <ycnian@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>