netsniff-ng: Unindent goto label

Stick to the usual style of having goto labels not indented.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
netsniff-ng: Remvoe unnecessary cast to void *

The iov_base member of struct iovec is already void *, so there is no
need to cast it.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>