base: disable the modem if up to N consecutive commands get timed out

This feature is initially disabled for all modems, but plugins can enable it by
setting a value greater than 0 for the "max-timeouts" property when creating the
modem object.

src/mm-modem-base.h

@@ -35,6 +35,8 @@
 typedef struct _MMModemBase MMModemBase;
 typedef struct _MMModemBaseClass MMModemBaseClass;
 
+#define MM_MODEM_BASE_MAX_TIMEOUTS   "max-timeouts"
+
 struct _MMModemBase {
     GObject parent;
 };