set init_on_free=0 as default cmdline kernel option for generic-x86_64

to get certain newer NUC systems to boot correctly again when doing a
UEFI boot (this fixes #2834).

buildroot-external/board/generic-x86_64/grub.cfg

@@ -17,7 +17,7 @@ else
   set default="0"
 fi
 
-default_cmdline="console=tty2 ro rootwait rootdelay=5 init_on_alloc=1 init_on_free=1 slab_nomerge net.ifnames=0 quiet loglevel=0"
+default_cmdline="console=tty2 ro rootwait rootdelay=5 init_on_alloc=1 init_on_free=0 slab_nomerge net.ifnames=0 quiet loglevel=0"
 file_env -f ($bootfs)/cmdline.txt cmdline
 
 # menu entry definitions