Topology repair may change btree node min/max keys: when it does so, we
need to always rebuild eytzinger search trees because nodes directly
depend on those values.

This fixes a bug found by the 'kill_btree_node' test, where we'd pop an
assertion in bch2_bset_search_linear().
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>