PlainTableFactory::PlainTableFactory() to have huge TLB turned off by default

Summary: PlainTableFactory::PlainTableFactory() now has Huge TLB page feature turned on by default. Although it is not a public API (which we always turn the feature off now), our unit tests, like db_test sometimes uses it directly, which causes wrong coverage of codes. This patch fix it to allow unit tests to run with the correct setting

Test Plan: Run db_test and make sure this feature is not on any more.

Reviewers: igor, haobo

Reviewed By: igor

CC: yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18483

table/plain_table_factory.h

@@ -63,7 +63,7 @@ class PlainTableFactory : public TableFactory {
                              int bloom_bits_per_key = 0,
                              double hash_table_ratio = 0.75,
                              size_t index_sparseness = 16,
-                             size_t huge_page_tlb_size = 2 * 1024 * 1024)
+                             size_t huge_page_tlb_size = 0)
       : user_key_len_(user_key_len),
         bloom_bits_per_key_(bloom_bits_per_key),
         hash_table_ratio_(hash_table_ratio),