netfilter: xt_qtaguid: extend iface stat to report protocols

In the past the iface_stat_fmt would only show global bytes/packets
for the skb-based numbers.
For stall detection in userspace, distinguishing tcp vs other protocols
makes it easier.
Now we report
  ifname total_skb_rx_bytes total_skb_rx_packets total_skb_tx_bytes
  total_skb_tx_packets {rx,tx}_{tcp,udp,ohter}_{bytes,packets}

Bug: 6818637
Signed-off-by: JP Abgrall <jpa@google.com>