babeld: remove useless kernel.h structs and constants.

These are useless in the Quagga environment.
babeld: use proper logging with zlog_err.
babeld: use streams for iterating over routes.
babeld: use streams for iterating over xroutes.
babeld: don't directly modify a neighbour in parse_hello_subtlv()
babeld: silently ignore unknown sub-TLVs

This is a MUST according to the Babel Extension Mechanism draft
(Section 2.2.3).
babeld: remove unused (and bad-written) function header.
babeld: fix typos in warning messages.
babeld: fix typo in send_update_resend.