Try booting up to 3 times on GRUB2 based systems (#2112)

* Retry up to 3 times

By default, HAOS used to retry 3 times. That is still true for U-Boot
based boards. Apply the same logic for GRUB2 based systems for
consistency.

This can help to remedy intermittent internet/connectivity issuese.
Altough hacky, in practise it makes sense to give the newly installed OS
another go.

* Also apply to generic-aarch64

buildroot-external/board/pc/grub.cfg

@@ -15,29 +15,43 @@ for SLOT in $ORDER; do
         INDEX=0
         OK=$A_OK
         TRY=$A_TRY
-        A_TRY=1
     fi
     if [ "$SLOT" == "B" ]; then
         INDEX=1
         OK=$B_OK
         TRY=$B_TRY
-        B_TRY=1
     fi
-    if [ "$OK" -eq 1 -a "$TRY" -eq 0 ]; then
+    if [ "$OK" -eq 1 -a "$TRY" -lt 3 ]; then
         default=$INDEX
+
+        # increment attempts and save back to slot
+        if [ "$TRY" -eq 1 ]; then
+            TRY=2
+        elif [ "$TRY" -eq 2 ]; then
+            TRY=3
+	else
+            TRY=1
+        fi
+
+	if [ "$SLOT" == "A" ]; then
+            A_TRY=$TRY
+        fi
+	if [ "$SLOT" == "B" ]; then
+            B_TRY=$TRY
+        fi
+
         break
     fi
 done
 
-# reset booted flags
+# No bootable slot found, choose rescue...
 if [ "$default" -eq 99 ]; then
-    if [ "$A_OK" -eq 1 -a "$A_TRY" -eq 1 ]; then
-        A_TRY=0
+    if [ "$A_OK" -eq 1 ]; then
+        default=2
     fi
-    if [ "$B_OK" -eq 1 -a "$B_TRY" -eq 1 ]; then
-        B_TRY=0
+    if [ "$B_OK" -eq 1 ]; then
+        default=3
     fi
-    default=0
 fi
 
 save_env A_TRY A_OK B_TRY B_OK ORDER MACHINE_ID