autoupdater: rename oneshot updates to fallback, improve handling for frequent runs

The oneshot update now won't be considered until 24h after the priority delay
has passed (so regular updates should have at least one chance to do the updates
even for PRIORITY=0 updates)

admin/autoupdater/files/usr/sbin/autoupdater

@@ -25,16 +25,16 @@ local old_version = util.trim(fs.readfile(settings.version_file) or '')
 -- the priority and even when it is disabled in uci
 local force = false
 
--- If oneshot is true the updater will perform an update only if the whole
--- timespan given by the priority has passed
-local oneshot = false
+-- If fallback is true the updater will perform an update only if the
+-- timespan given by the priority and another 24h have passed
+local fallback = false
 
 
 for _, a in ipairs(arg) do
   if a == '-f' then
     force = true
-  elseif a == '-o' then
-    oneshot = true
+  elseif a == '--fallback' then
+    fallback = true
   end
 end
 
@@ -182,12 +182,19 @@ local function get_probability(date, priority)
     else
       -- Will give 1 when priority == 0, and lower probabilities the higher the priority value is
       -- (similar to the old static probability system)
-      return 0.9^priority
+      return 0.75^priority
     end
+
+  elseif fallback then
+    if diff >= seconds + 86400 then
+      return 1
+    else
+      return 0
+    end
+
   elseif diff >= seconds then
     return 1
-  elseif oneshot then
-    return 0
+
   else
     local x = diff/seconds
     -- This is the most simple polynomial with value 0 at 0, 1 at 1, and whose first derivative is 0 at both 0 and 1