libceph: fix authorizer invalidation, take 2

libceph: fix authorizer invalidation, take 2

Back in 2013, commit d49ef080c5ae ("libceph: fix authorizer
invalidation") tried to fix authorizer invalidation issues by clearing
validity field.  However, nothing ever consults this field, so it
doesn't force us to request any new secrets in any way and therefore we
never get out of the exponential backoff mode:

    [  129.973812] libceph: osd2 192.168.122.1:6810 connect authorization failure
    [  130.706785] libceph: osd2 192.168.122.1:6810 connect authorization failure
    [  131.710088] libceph: osd2 192.168.122.1:6810 connect authorization failure
    [  133.708321] libceph: osd2 192.168.122.1:6810 connect authorization failure
    [  137.706598] libceph: osd2 192.168.122.1:6810 connect authorization failure
    ...

AFAICT this was the case at the time d49ef080c5ae was merged, too.

Using timespec solely as a bool isn't nice, so introduce a new have_key
flag, specifically for this purpose.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>