Prevent "incompatible license" error.

grub-core/net/drivers/ieee1275/ofnet.c

@@ -6,6 +6,8 @@
 #include <grub/net.h>
 #include <grub/time.h>
 
+GRUB_MOD_LICENSE ("GPLv3+");
+
 static grub_err_t 
 card_open (struct grub_net_card *dev)
 {

grub-core/net/net.c

@@ -27,6 +27,8 @@
 #include <grub/command.h>
 #include <grub/env.h>
 
+GRUB_MOD_LICENSE ("GPLv3+");
+
 struct grub_net_route
 {
   struct grub_net_route *next;

grub-core/net/tftp.c

@@ -9,6 +9,8 @@
 #include <grub/dl.h>
 #include <grub/file.h>
 
+GRUB_MOD_LICENSE ("GPLv3+");
+
 static grub_err_t 
 tftp_open (struct grub_file *file, const char *filename)
 {