net/net: Convert parse_host_port() to Error

Cc: berrange@redhat.com
Cc: kraxel@redhat.com
Cc: pbonzini@redhat.com
Cc: jasowang@redhat.com
Cc: armbru@redhat.com
Cc: eblake@redhat.com
Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>