Redis Redis Cluster crashes on certain armhf platforms.

This is a result of unaligned memory access which results with SIGBUS on certain armhf (armv7l) platforms, in some configurations. This does not reproduce on all platforms (e.g. RaspberryPi 4 with Raspbian seems OK).

Crash is a result of clusterReadHandler() using an sds buffer and passing an unaligned clusterMsg * pointer to clusterProcessPacket(). Code should be refactored to use a simple buffer and not an sds to maintain memory alignment.