libnuma: Fix incorrect print and exit of numa_preferred/_many APIs

Only when policy is preferred, numa_bitmask_weight will be judged,
because mbind and preferred_many support multiple nodes.

fixes: 87c6834("libnuma: Convert preferred node into a mask")

Signed-off-by: Chunsheng Luo <luochunsheng@ustc.edu>

libnuma.c

@@ -1882,7 +1882,7 @@ static struct bitmask *__numa_preferred(void)
 			policy != MPOL_BIND)
 		return bmp;
 
-	if (numa_bitmask_weight(bmp) > 1) {
+	if (policy == MPOL_PREFERRED && numa_bitmask_weight(bmp) > 1) {
 		errno = EINVAL;
 		numa_error(__FILE__);
 	}