LU-15689 libcfs: libcfs_debug_mb set incorrectly on init

LU-15689 libcfs: libcfs_debug_mb set incorrectly on init

If libcfs_debug_mb parameter is specified to insmod (i.e. set before
module is initialized) then it does not get initialized correctly.

libcfs_param_debug_mb_set() expects cfs_trace_get_debug_mb() to return
zero if the module has not been initialized yet, but
cfs_trace_get_debug_mb() will return 1 in this case. Modify
cfs_trace_get_debug_mb() to return zero as expected. A related issue
is that in this case we need to call cfs_trace_get_debug_mb() after
cfs_tracefile_init() so that libcfs_debug_mb gets the same value it
would get if we had set it after module init.

When libcfs_debug_mb is specified to insmod, libcfs_debug_init()
divides its value by num_possible_cpus(), but this is already done in
libcfs_param_debug_mb_set().

Test-Parameters: trivial
Fixes: 8b78a3ffb5 ("LU-9859 libcfs: always range-check libcfs_debug_mb setting.")
HPE-bug-id: LUS-10839
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I1003758156acb5cf6ea30bbdfd7b45a743a2a5aa
Reviewed-on: https://review.whamcloud.com/46925
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>