osdc/Objecter: reinstate _recalc_linger_op_target

This got overwritten by _calc_target in 8a6c8f08 (objecter: a major
refactoring).  Its behaviour could be relevant to #9112

Signed-off-by: John Spray <john.spray@redhat.com>
librados: separate ::notify return values

There is a return code from objecter for committing
the notify linger op, and then later a code in the
CEPH_MSG_WATCH_NOTIFY handled by RadosClient directly.
Afaict there isn't any nice ordering guarantee here,
so they could stamp on each other.  Use a SaferCond
for the submit one.

I don't think this was related to #9112 but while
I'm here...

Signed-off-by: John Spray <john.spray@redhat.com>
osdc/Objecter: fix session linger_ops indexing

It was supposed to be a map of linger ID, but
in 8a6c8f08 one of the insertions was changed
to use the current op's TID.

Signed-off-by: John Spray <john.spray@redhat.com>