calibre: increase no-activity timeout (#13846)

Calibre does not send the expected regular "NOOP" pings during
its "Analyzing books on the device…" phase, and that operation
can take a long time (75s for 4500 books on a recent machine).

plugins/calibre.koplugin/wireless.lua

@@ -337,7 +337,7 @@ function CalibreWireless:connect()
 
     -- Heartbeat monitoring…
     while ok and not self.disconnected_by_server do
-        ok = resume_in(15)
+        ok = resume_in(5 * 60)
     end
 
     local msg