ipset: Fix malformed output from list/save for ICMP types in port field.

ipset: Fix malformed output from list/save for ICMP types in port field.

Found with ipset 6.12.1, but upstream version is still affected.

Creating set of dimension three, adding elements to it and then
displaying gives following results:
-----------------------------------

 # ipset create test-1 hash:ip,port,ip
 # ipset add test-1 192.0.2.1,icmp:echo-request,192.0.2.1
 # ipset add test-1 192.0.2.1,icmp:ttl-zero-during-reassembly,192.0.2.1
 # ipset list test-1
 Name: test-1
 Type: hash:ip,port,ip
 Header: family inet hashsize 1024 maxelem 65536
 Size in memory: 16608
 References: 0
 Members:
 192.0.2.1,icmp:ttl-zero-during-reass,192.0.2.1
 192.0.2.1,icmp:echo-re,192.0.2.1

Same results with -output save|xml.

ipset_print_proto_port() from lib/print.c returns incorrect length
of printed string when ICMP/ICMPv6 specified in port field.

Signed-off-by: Sergey Popovich <popovich_sergei@mail.ru>
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>