bcachefs: get_update_rebalance_opts()

bcachefs: get_update_rebalance_opts()

bch2_move_get_io_opts() now synchronizes options loaded from the
filesystem and inode (if present, i.e. not walking the reflink btree
directly) with options from the bch_extent_rebalance_entry, updating the
extent if necessary.

Since bch_extent_rebalance tracks where its option came from we can
preserve "inode options override filesystem options", even for indirect
extents where we don't have access to the inode the options came from.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>