Comment 5 for bug 1918936

Per discussion on Mattermost, the original behavior was to try string_to_u16() before parse_portname(). This was switched in upstream commit https://git.netfilter.org/ipset/tree/lib/parse.c?id=516600858cb54906fb728d04e5edf1131ee7b3b2 and released with ipset v6.37.