py: Change MP_UNARY_OP_INT to MP_UNARY_OP_INT_MAYBE.

To be consistent with MP_UNARY_OP_INT_FLOAT and MP_UNARY_OP_INT_COMPLEX,
and allow int() to first check if a type supports __int__ before trying
other things (as per CPython).

Signed-off-by: Damien George <damien@micropython.org>

py/objint_longlong.c

@@ -119,6 +119,8 @@ mp_obj_t mp_obj_int_unary_op(mp_unary_op_t op, mp_obj_t o_in) {
             self->val = -self->val;
             return MP_OBJ_FROM_PTR(self);
         }
+        case MP_UNARY_OP_INT_MAYBE:
+            return o_in;
         default:
             return MP_OBJ_NULL;      // op not supported
     }