lsfd: collect the device number for mqueue fs in the initialization stage

lsfd: collect the device number for mqueue fs in the initialization stage

Though lsfd reads device minor numbers for file-systems having "nodev"
from /proc/$pid/mountinfo, we observed lsfd failed to resolve the
values of SOURCE column for mqueue files on s390 CI/CD env. It seems
that /proc/$pid/mountinfo doesn't provide enough information.

This change makes lsfd open a mqueue file in lsfd's initialization
stage as a new data source for resolving; lsfd can collect an
actually-used minor number from the file descriptor with fstat(2).

Signed-off-by: Masatake YAMATO <yamato@redhat.com>