trace: do not remove icmp type from packet dump

trace: do not remove icmp type from packet dump

As of 0.9.8 the icmp type is marked as a protocol field, so its
elided in 'nft monitor trace' output:

   icmp code 0 icmp id 44380 ..

Restore it.  Unlike tcp, where 'tcp sport' et. al in the dump
will make the 'ip protocol tcp' redundant this case isn't obvious
in the icmp case:

  icmp type 8 code 0 id ...

Reported-by: Martin Gignac <martin.gignac@gmail.com>
Fixes: 98b871512c4677 ("src: add auto-dependencies for ipv4 icmp")
Signed-off-by: Florian Westphal <fw@strlen.de>