Use FTDM_SIZE_FMT where needed, don't treat ftdm_event_t as an int
(even if the e_type enum is the first member), datalen vs. *datalen fix
and other warnings.

All reported by __check_printf() (GCC + __attribute__((format(printf,x,y))) ).
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>