[bug] udhcpc support is incomplete

[holmanb]

Steps to reproduce the problem

PR #4190 introduced udhcpc client support. As it is, udhcpc may work on some platforms, but is missing support for unknown dhcp options. This is used by microsoft azure to update the wireserver IP address via option 245. I believe that this is still a requirement, so this should be implemented for udhcpc as well for correct behavior on Microsoft Azure.

[holmanb]

I believe that this is still a requirement

@cjp256 can you please confirm?

[holmanb]

@jfroche In #4190 you said you would follow up to complete udhcpc support. Are you still planning to do that?

[cjp256]

Yes, we do try and honor it. Though I can't say with certainty it's actively used to change the default IP in any case today.