Generate Qsearch checks only at depth 0

An old idea retested at SPRT(0, 3) with 60+0.05 TC:
LLR: 2.95 (-2.94,2.94) [0.00,3.00]
Total: 98872 W: 15549 L: 15123 D: 68200

This is a very small elo increase patch so it really
stresses the limits of fishtest.

bench: 8596156

src/types.h

@@ -194,8 +194,8 @@ enum Depth {
   ONE_PLY = 2,
 
   DEPTH_ZERO          =  0 * ONE_PLY,
-  DEPTH_QS_CHECKS     = -1 * ONE_PLY,
-  DEPTH_QS_NO_CHECKS  = -2 * ONE_PLY,
+  DEPTH_QS_CHECKS     =  0 * ONE_PLY,
+  DEPTH_QS_NO_CHECKS  = -1 * ONE_PLY,
   DEPTH_QS_RECAPTURES = -5 * ONE_PLY,
 
   DEPTH_NONE = -127 * ONE_PLY