PG: mark_log_for_rewrite on resurrection

Fixes: #8777
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
(cherry picked from commit 8346e10755027e982f26bab4642334fd91cc31aa)
PG::can_discard_op: do discard old subopreplies

Otherwise, a sub_op_reply from a previous interval can stick around
until we either one day go active again and get rid of it or delete the
pg which is holding it on its waiting_for_active list.  While it sticks
around futily waiting for the pg to once more go active, it will cause
harmless slow request warnings.

Fixes: #9259
Backport: firefly
Signed-off-by: Samuel Just <sam.just@inktank.com>
(cherry picked from commit ae3d87348ca4e2dde809c9593b0d54ce0469f7a0)