This is another step in a general cleanup of the state machine.  To
help me knowning what is audited and what is not, I rename the "common
functions" to fsm-lib. This is the management of announce.

- master and slave functions were the same, so they are unified now

- hooks->handle_annunce returns int (it may fail)
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>