gateway: fix segment fault when closing all connections incorrectly.

We should directly call sheep_del_sockfd() to destroy all the connections or
memmove will cause segment fault.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
script: update Makefile.am to remove {start, stop}-sheepdog

This fix a compile error.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>