fix compile with android-ndk for missing socket.h
replace bcmp with own binary compare method

fixes compile error on android-ndk, which seem to not have bcmp implemented
prl: resolve PRL names to addresses suitable for UDP instead of IPv6-in-IP

on my android device, getaddrinfo for IPv4 addresses for IPPROTO_IPV6 returns
an empty list. Because we only care for the IPv4 address here and not the actual
protocol, try to resolve addresses suitable for UDP. The result is a working
isatapd on android (cm-10.2).
accept parameter value 'auto' for --name, --link and --interval

options name, link and interval accept parameter value 'auto', which will
effectively ignore the parameter. Useful for startup scripts that read
configuration values from a configuration file.

isatapd --link auto --name auto --interval auto
man: update man page to reflect availability of 'auto' for some parameters