src/: Rename `udpsocket' and `nudp' (style)

[adns] / regress / init-ndots.text

nameserver 172.18.45.6
sortlist 127.0.0.1/32 172.18.45.0/28 172.18.45.0/24
search davenant.greenend.org.uk greenend.org.uk
options ndots:3