block/iscsi: statically link qemu_iscsi_opts

commit f57b4b5f moved qemu_iscsi_opts into vl.c. This
made them invisible for qemu-img, qemu-nbd etc.

Fixes: f57b4b5f
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <1485262161-18543-1-git-send-email-pl@kamp.de>
[Drop useless #ifdef. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>