Rover: Doubled the rate at which read_control_switch is called.

As the previous commit as doubled the number of reads required to
confirm that the mode change switch has been changed this means it
will halve the speed it changes at.  So we double the rate at which we
read it to keep things consistent.

APMrover2/APMrover2.cpp

@@ -61,7 +61,7 @@ const AP_Scheduler::Task Rover::scheduler_tasks[] PROGMEM = {
     { SCHED_TASK(gcs_retry_deferred),     1,   1000 },
     { SCHED_TASK(gcs_update),             1,   1700 },
     { SCHED_TASK(gcs_data_stream_send),   1,   3000 },
-    { SCHED_TASK(read_control_switch),   15,   1000 },
+    { SCHED_TASK(read_control_switch),    7,   1000 },
     { SCHED_TASK(read_trim_switch),       5,   1000 },
     { SCHED_TASK(read_battery),           5,   1000 },
     { SCHED_TASK(read_receiver_rssi),     5,   1000 },