There doesn't seem to be a reason not to check the filter. Update
and extend the test. Currently the filter function will be called
once for the log check and once for the output of it.
This commit adds OSMO_ASSERTs for mandatory conditions related to
log_check_level, and fprintfs for optional conditions, since it is
always safe for log_check_level to return != 0.
Sponsored-by: On-Waves ehf
The filter_fn has not been copied into the new structure breaking
the imsi and other filters in OpenBSC. Looking at the code we should
also introduce a callback for the reset of the context so we could
use subscr_get/subscr_put on the subscriber structure.