Add d_logp explicit subsystem log predicate.

The idea is, dlog_p(ceph_subsys_foo, level) is true iff the gather
level of ceph_subsys_foo is greater than level.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Debug cleanups in Xio.

Use the new dlog_p macro in XioPortal.h.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Merge branch 'xio-firefly-cmake-multi-ref' of https://github.com/linuxbox2/linuxbox-ceph into xio-firefly-cmake-multi-ref
Move Xio tracing selector into Ceph loglevl 15.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>