msg: hexdump messages we can't decode at configurable debug level

We had this hard-coded to 30.  Make it tunable.

Signed-off-by: Sage Weil <sage@redhat.com>
msg: hexdump bad messages at debug level 1 (not 30)

These are rare, and when they do happen, we want to see them in the
logs.

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2513 from ceph/wip-decode-dump

msg: dump messages we can' decode at a low devel level

Reviewed-by: Greg Farnum <greg@inktank.com>