dog: check the result of dog_exec_req() correctly

dog_exec_req doesn't return a result code after the commit 5940548.
We have to check rsp->result instead of its return value.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
dog: add more result check of dog_collie_exec()

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
dog: fix send_light_req

This patch fixes segfault of many dog commands due to commit a4d01de

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Reviewed-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>