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>
netfilter: xt_qtaguid: Allow tracking loopback

In the past it would always ignore interfaces with loopback addresses.
Now we just treat them like any other.
This also helps with writing tests that check for the presence
of the qtaguid module.

Signed-off-by: JP Abgrall <jpa@google.com>
netfilter: qtaguid: rate limit some of the printks

Some of the printks are in the packet handling path.
We now ratelimit the very unlikely errors to avoid
kmsg spamming.

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