bfd: fix bfd_key_id update

bfd: fix bfd_key_id update

Type: fix

Currently, auth activation CLI command
"bfd upd session auth activate ... conf-key-id <cki> bfd-key-id <bki>"
allows to change both key-ids to new values at once.
But if only bfd-key-id should be corrected, e.g. as a result of mistyping,
we can't do that in a single operation, and have to deactivate auth first
and then reactivate it with a correctly entered pair of ids.

Currently, backend's bfd_auth_activate() function returns immediately,
with no action, if it finds that submitted conf-key-id matches the
current record. No check on bfd-key-id value is made.

With this fix, bfd_auth_activate() checks if session's bfd-key-id has to
be changed to a new value, and if so, it updates and logs appropriately.

Change-Id: I3b915a936cb1721707860bb503f70e7dd29e0ddd
Signed-off-by: Alexander Skorichenko <askorichenko@netgate.com>