rocksdb: pull up to master (4.12 + a few patches)

This includes Somnath's fix for log recycling.

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/src/rocksdb b/src/rocksdb
index 6797e6ffacd90470140f64cea068970bb3a30aaf..1d980a8e357d0df318c12b1f5ee6b0ae91d7aeb8 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit 6797e6ffacd90470140f64cea068970bb3a30aaf
+Subproject commit 1d980a8e357d0df318c12b1f5ee6b0ae91d7aeb8