Watchdog: fixes "off-by-one" error
'man sssd.conf': timeout: "Note that after three missed heartbeats
the process will terminate itself."
But implementation was:
```
\#define WATCHDOG_MAX_TICKS 3
...
if (__sync_add_and_fetch(&watchdog_ctx.ticks, 1) > WATCHDOG_MAX_TICKS) {
...
_exit(1);
```
-- since after reset ticks start from 0 effectively this was 4 heartbeats.
Fixed to match man page.
Resolves: https://pagure.io/SSSD/sssd/issue/4169
Reviewed-by: Pavel Březina <pbrezina@redhat.com>