Default G30 to engage / disengage

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)                          { return seenval(c) ? value_bool()         : seen(c); }
+  FORCE_INLINE static bool     boolval(const char c, const bool dval=false)   { return seenval(c) ? value_bool()         : (seen(c) ? true : dval); }
   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)
- *   E   Engage the probe for each probe
+ *   E   Engage the probe for each probe (default 1)
  */
 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 ProbePtRaise raise_after = parser.boolval('E') ? PROBE_PT_STOW : PROBE_PT_NONE;
+  const ProbePtRaise raise_after = parser.boolval('E', true) ? PROBE_PT_STOW : PROBE_PT_NONE;
   const float measured_z = probe_pt(xpos, ypos, raise_after, 1);
 
   if (!isnan(measured_z)) {