redis: bump to version 2.6.17

Fixes since 2.6.16:
* [FIX] redis-cli: fix big keys search when the key no longer exist.
* [FIX] Allow AUTH / PING when disconnected from slave with serve-stale-data on.
* [FIX] redis-benchmark: update help for new __rand_int__ form.
* [FIX] Fix broken rdbWriteRaw() return value check in rdb.c (harmless).
* [FIX] Log to what master a slave is going to connect to.
* [FIX] Only run the fast active expire cycle if master & enabled.
* [FIX] Fixed a replication bug involving 32 bit instances and big datasets
        hard to compress that resulted into more than 2GB of RDB file sent.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>