res_pjsip_logger: Preserve logging state on reloads.

res_pjsip_logger: Preserve logging state on reloads.

Currently, reloading res_pjsip will cause logging
to be disabled. This is because logging can also
be controlled via the debug option in pjsip.conf
and this defaults to "no".

To improve this, logging is no longer disabled on
reloads if logging had not been previously
enabled using the debug option from the config.
This ensures that logging enabled from the CLI
will persist through a reload.

ASTERISK-29912 #close

Resolves: #246

UserNote: Issuing "pjsip reload" will no longer disable
logging if it was previously enabled from the CLI.