Objecter: pg_interval_t::is_new_interval needs pgid from previous pool

Objecter: pg_interval_t::is_new_interval needs pgid from previous pool

When increasing the pg_num of a pool, an assert would fail since the
calculated pgid seed would be for the pool's new pg_num value instead
of the previous pg_num value.

Fixes: #10399
Backport: infernalis, hammer, firefly
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit f20f7a23e913d09cc7fc22fb3df07f9938ddc144)

Conflicts: (hobject_t sort order not backported, trivial resolution)
	src/osdc/Objecter.cc
	src/osdc/Objecter.h