[Crash-utility] RFE: add '-l' option to dmesg command

[Dave Wysochanski]

It would be useful to have the ability to dump out only certain log
levels of the kernel log.  I know dmesg has '-m' which prepends the log
level and then you can always use some script logic but would it be easy
to add another option in crash to do this automatically?

-l level  Only display log messages matching 'level', which may be specified as a single number (3) or a range (0-3).