[odhcpd] Vendor-specific information option

[Kevin Vigouroux]

In the end, I think I understood the concepts.

I think I can use blob objects to simplify things. Moreover, it seems that we
can pass a pointer to any memory area to manage several instances of the
vendor-specific information option using an abstraction as with IOV_NTP and
IOV_NTP_ADDR[1].

I would publish my code on a new vendor-opts branch [2]. If I'm satisfied, I'll
make a pull request.

[1] https://github.com/openwrt/odhcpd/blob/master/src/dhcpv6.c#L557
[2] https://github.com/gilaro/odhcpd/tree/vendor-opts
-- 
Best regards,
Kevin Vigouroux