scripts/check-logging: verify log setup

run by makefile when 'sudo make setuid' is considered
verifies log config and parameters present

else suggests running 'sudo make log'
log config: increase rate limits

RTAPI startup pushes the limits of rsyslog default rate limiting.
Increase the burst limit so no messages get dropped.
src/Makefile: verify logging works, add 'log' target

'sudo make log' will install a working rsyslog config fragment
and restart rsyslog