delinearize: list the icmpx reason with the string associated

delinearize: list the icmpx reason with the string associated

If you add the rule:
  nft add rule inet filter input reject with icmpx type host-unreachable
  nft list table inet filter

shows:
  table inet filter {
	chain input {
		reject with icmpx type 2
	}
  }

We have to attach the icmpx datatype when we list the rules that use it. With
this patch if we list the ruleset, the output is:

  table inet filter {
	chain input {
		reject with icmpx type host-unreachable
	}
  }

Signed-off-by: Alvaro Neira Ayuso <alvaroneay@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>