extensive orb_advert_t fixes

The calls to orb_advertise were being mishandled throughout the code.
There were ::close() calls on memory pointers, there were checks
against < 0 when it is a pointer to a object and values larger than
0x7ffffffff are valid. Some places orb_advert_t variables were
being initialized as 0 other places as -1.

The orb_advert_t type was changed to uintptr_t so the pointer value
would not be wrapped as a negative number. This was causing a failure
on ARM.

Tests for < 0 were changed to == 0 since a null pointer is the valid
representation for error, or uninitialized.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/mavlink/mavlink_parameters.cpp

@@ -45,7 +45,7 @@
 
 MavlinkParametersManager::MavlinkParametersManager(Mavlink *mavlink) : MavlinkStream(mavlink),
 	_send_all_index(-1),
-	_rc_param_map_pub(-1),
+	_rc_param_map_pub(0),
 	_rc_param_map()
 {
 }
@@ -162,7 +162,7 @@ MavlinkParametersManager::handle_message(const mavlink_message_t *msg)
 				}
 				_rc_param_map.timestamp = hrt_absolute_time();
 
-				if (_rc_param_map_pub < 0) {
+				if (_rc_param_map_pub == 0) {
 					_rc_param_map_pub = orb_advertise(ORB_ID(rc_parameter_map), &_rc_param_map);
 
 				} else {