boolval revisited (#8016)

Marlin/src/gcode/calibrate/G33.cpp

     return;
   }
 
-  const bool towers_set           = parser.boolval('T', true),
+  const bool towers_set           = !parser.boolval('T'),
              stow_after_each      = parser.boolval('E'),
              _0p_calibration      = probe_points == 0,
              _1p_calibration      = probe_points == 1,

Marlin/src/gcode/eeprom/M500-M503.cpp

    * M503: print settings currently in memory
    */
   void GcodeSuite::M503() {
-    (void)settings.report(!parser.boolval('S', true));
+    (void)settings.report(parser.boolval('S'));
   }
 
 #endif // !DISABLE_M503

Marlin/src/gcode/parser.h

 
   // Provide simple value accessors with default option
   FORCE_INLINE static float    floatval(const char c, const float dval=0.0)   { return seenval(c) ? value_float()        : dval; }
-  FORCE_INLINE static bool     boolval(const char c, const bool dval=false)   { return seen(c)    ? value_bool()         : dval; }
+  FORCE_INLINE static bool     boolval(const char c)                          { return seenval(c) ? value_bool()      : seen(c); }
   FORCE_INLINE static uint8_t  byteval(const char c, const uint8_t dval=0)    { return seenval(c) ? value_byte()         : dval; }
   FORCE_INLINE static int16_t  intval(const char c, const int16_t dval=0)     { return seenval(c) ? value_int()          : dval; }
   FORCE_INLINE static uint16_t ushortval(const char c, const uint16_t dval=0) { return seenval(c) ? value_ushort()       : dval; }

Marlin/src/gcode/probe/G30.cpp

  *
  *   X   Probe X position (default current X)
  *   Y   Probe Y position (default current Y)
- *   S0  Leave the probe deployed
+ *   E   Engage the probe for each probe
  */
 void GcodeSuite::G30() {
   const float xpos = parser.linearval('X', current_position[X_AXIS] + X_PROBE_OFFSET_FROM_EXTRUDER),
 
   setup_for_endstop_or_probe_move();
 
-  const float measured_z = probe_pt(xpos, ypos, parser.boolval('S', true), 1);
+  const float measured_z = probe_pt(xpos, ypos, parser.boolval('E'), 1);
 
   if (!isnan(measured_z)) {
     SERIAL_PROTOCOLPAIR("Bed X: ", FIXFLOAT(xpos));