Add hooks in the correct places so the BFD daemon uses the data plane
instead of the software packet sending implementation to monitor the
session.
This code also adds some handlers to support fallback to FRR BFD session
handling, however since this complicates the code it won't work at the
moment (the BFD sockets are disabled by default when using data plane).
Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>