osdc/Objecter: _calc_target on all ops so that we notice splits

osdc/Objecter: _calc_target on all ops so that we notice splits

We need to make sure we update the mapping and get an accurate actual_pgid
value by recalcuating the mapping on every map change.  Otherwise, we may
not notice a split (and subsequent actual_pgid change) and resend the same
op with a stale spg_t.  To fix this,

- _calc_target on need_resend
- update target regardless of current con

Signed-off-by: Sage Weil <sage@redhat.com>