trace group defiined for shared_rng

Unittests fixed

2 mbedtls functions were updated to reflect the api

features/mbedtls/platform/src/shared_rng.cpp

@@ -24,6 +24,8 @@
 
 #include "mbed_trace.h"
 
+#define TRACE_GROUP "SRNG"
+
 mbedtls_hmac_drbg_context global_hmac_drbg;
 mbedtls_entropy_context global_entropy;
 static bool is_initialized = false;

features/nanostack/coap-service/test/coap-service/unittest/stub/mbedtls_stub.c

@@ -260,7 +260,7 @@ void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx )
 }
 
 int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
-                    mbedtls_md_handle_t md_info,
+                            const mbedtls_md_info_t * md_info,
                             int (*f_entropy)(void *, unsigned char *, size_t),
                             void *p_entropy,
                             const unsigned char *custom,
@@ -275,7 +275,7 @@ int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len
 }
 
 // from md.h
-mbedtls_md_handle_t mbedtls_md_info_from_type( mbedtls_md_type_t md_type )
+const mbedtls_md_info_t *mbedtls_md_info_from_type( mbedtls_md_type_t md_type )
 {
     return 0;
 }