net/tls: change default cache entry number
This commit minimizes the default maximum entry count for memory saving.
/* SSL Cache options */
//#define MBEDTLS_SSL_CACHE_DEFAULT_TIMEOUT 86400 /**< 1 day */
-//#define MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES 50 /**< Maximum entries in cache */
+#define MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES 2 /**< Maximum entries in cache */
/* SSL options */
//#define MBEDTLS_SSL_MAX_CONTENT_LEN 16384 /**< Maxium fragment length in bytes, determines the size of each of the two internal I/O buffers */
