Enabled DEBUG_WOLFSSL_MALLOC by default

Checking for memory allocation failures is essential and should never
be disabled. This increases the binary size only minimally.

E.g. performance impact on the C6:
 * binary size increases by 14864 bytes
 * free heap is reduced by 8 bytes

port/user_settings.h

@@ -141,7 +141,7 @@
 
 /* Full debugging turned off, but show malloc failure detail */
 /* #define DEBUG_WOLFSSL */
-// #define DEBUG_WOLFSSL_MALLOC
+#define DEBUG_WOLFSSL_MALLOC
 
 /* RSA_LOW_MEM: Half as much memory but twice as slow. */
 #define RSA_LOW_MEM