Fix crash recovery with small buffer pool

Occasionally, the test innodb_gis.rtree_recovery,4k runs out of
buffer pool during crash recovery.

This test might have started failing in connection with MDEV-18726.
Work around it by reserving a little more overhead for the recovery
hash tables.

FIXME: Propagate the "out of memory" error to recv_add_to_hash_table()
and transition to multi-batch recovery with a finer granularity.

storage/innobase/log/log0recv.cc

@@ -601,7 +601,7 @@ recv_sys_var_init(void)
 	recv_previous_parsed_rec_type = MLOG_SINGLE_REC_FLAG;
 	recv_previous_parsed_rec_offset	= 0;
 	recv_previous_parsed_rec_is_multi = 0;
-	recv_n_pool_free_frames	= 256;
+	recv_n_pool_free_frames	= 384;
 	recv_max_page_lsn = 0;
 }