net/bootp: Fix uninitialized scalar variable

In the function grub_net_configure_by_dhcp_ack(),
grub_net_network_level_address_t addr is called but isn't being initialized.
This results in the member grub_dns_option_t option being filled with junk data
from the stack. To prevent this, we can set the option member in addr to 0.

Fixes: CID 375036

Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/net/bootp.c

@@ -244,6 +244,7 @@ grub_net_configure_by_dhcp_ack (const char *name,
 
   addr.type = GRUB_NET_NETWORK_LEVEL_PROTOCOL_IPV4;
   addr.ipv4 = bp->your_ip;
+  addr.option = 0;
 
   if (device)
     *device = 0;