bs_sheepdog.c: fix a descriptor leak in connect_to_sdog_tcp()

When connect_to_sdoc_tcp function failed to connect a socket due to an
error other than EINTR, it doesn't free the socket file descriptor.

This fixes the leak bug.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>