rds: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break statements instead of
letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>