util.c: Don't byte-swap IPv4 addresses, even if we don't have IPv6.

The `string_item_to_ipaddr' function returns addresses as a single
integer in host byte order.  But this isn't what's wanted for setting up
`struct sockaddr_in', for example.  The function `adns_text2addr' does
the right thing.

I think this has always been wrong for setting up UDP sockets: before
the introduction of `string_item_to_iaddr', `udp_apply' would call
`string_item_to_ipaddr' directly, and neglected to swap the bytes.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>