CTR_DRBG: explicitly set entropy_nonce_len=0 when desired

No behavior change. Prepare for a future version that will set the
entropy nonce length to a nonzero value by default.
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 8a62f6d..8c6ee59 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -732,6 +732,7 @@
 
     test_offset = 0;
     mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     CHK( mbedtls_ctr_drbg_seed( &ctx,
                                 ctr_drbg_self_test_entropy,
                                 (void *) entropy_source_pr,
@@ -756,6 +757,7 @@
 
     test_offset = 0;
     mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     CHK( mbedtls_ctr_drbg_seed( &ctx,
                                 ctr_drbg_self_test_entropy,
                                 (void *) entropy_source_nopr,
diff --git a/tests/suites/test_suite_ctr_drbg.function b/tests/suites/test_suite_ctr_drbg.function
index 02f9eca..c79b6e2 100644
--- a/tests/suites/test_suite_ctr_drbg.function
+++ b/tests/suites/test_suite_ctr_drbg.function
@@ -45,6 +45,7 @@
     /* CTR_DRBG_Instantiate(entropy[:entropy->len], nonce, perso, <ignored>)
      * where nonce||perso = nonce[nonce->len] */
     mbedtls_ctr_drbg_set_entropy_len( &ctx, entropy_chunk_len );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     TEST_ASSERT( mbedtls_ctr_drbg_seed(
                      &ctx,
                      mbedtls_test_entropy_func, entropy->x,