[Keyboard] Change RGB light defaults for melgeek/mj6xy (#13657)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/melgeek/mj6xy/rev3/config.h

@@ -42,6 +42,8 @@
 
 #ifdef RGB_DI_PIN
 #    define RGBLIGHT_ANIMATIONS
+#    define RGBLIGHT_DEFAULT_MODE (RGBLIGHT_EFFECT_RAINBOW_MOOD + 6) 
+#    define RGBLIGHT_DEFAULT_SPD 10
 #	 define RGBLED_NUM        16
 #    define RGBLIGHT_HUE_STEP 8
 #    define RGBLIGHT_SAT_STEP 8