Unexpected resync with master

This issue is based on "redis doesn't close replication fd", so it can call syncWithMaster with previous replication fd.

There are 2 approaches.

1] when client requests "slaveof" command
 -> closeing replication fd.
 
2] when syncWithMaster call
-> checking fd is repl_transfer_s

and if repl_state == REDIS_REPL_CONNECTED , then redis doesn't close replication fd.