util.jid: Fix to reject IPv6 literal hosts without brackets From RFC 7622: > Implementation Note: Reuse of the IP-literal rule from [RFC6874] > implies that IPv6 addresses are enclosed within square brackets (i.e., > beginning with '[' and ending with ']'), , which was not the case with > the definition of the XMPP address format in [RFC3920] but which was > changed in [RFC6122].