HIPL generates UPDATE without setting preferred bit

[Miika Komu]

Jeff Ahrenholz suggested that we should set the preferred bit in UPDATE. Please see the discussion thread:

http://www.freelists.org/post/hipl-dev/interop-with-OpenHIP-failing-due-to-UPDATE-packets

[Miika Komu (miika-iki)]

Some cristicism against the preferred bit in section III.B:

http://www.cs.helsinki.fi/u/gurtov/papers/softcom09.pdf

It should be noted that the preferred bit stuff is in RFC5206. Hence, we should simply conform to it (and perhaps try to pass the change to RFC5206-bis).