odhcp6c: new package

Signed-off-by: Alexander Clouter <alex+buildroot@digriz.org.uk>
[ThomasDS: needs ipv6; rewrap package/odhcp6c/Config.in]
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Tested-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
(compile-tested on x86/glibc, armel/glibc, armel/uclibc)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>