In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 114763
Addresses-Coverity-ID: 114764
Addresses-Coverity-ID: 114765
Addresses-Coverity-ID: 114766
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>