Allow configuration of read timeouts at compile-time

Introduces compile-time constants
- MBEDTLS_SSL_CONF_READ_TIMEOUT
- MBEDTLS_SSL_CONF_HS_TIMEOUT_MIN
- MBEDTLS_SSL_CONF_HS_TIMEOUT_MAX
which allow to configure the read timeouts and
minimum/maximum handshake timeout at compile time.

Impact on code-size:

|  | GCC 8.2.1 | ARMC5 5.06 | ARMC6 6.12 |
| --- | --- | --- | --- |
| `libmbedtls.a` before  | 23147 | 23781 | 26703 |
| `libmbedtls.a` after | 23131 | 23753 | 26673 |
| gain in Bytes | 16 | 28 | 30 |
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 57fe486..093c4ac 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -1085,6 +1085,53 @@
  * be fixed at compile time via one of MBEDTLS_SSL_SSL_CONF_XXX.
  */
 
+#if !defined(MBEDTLS_SSL_CONF_READ_TIMEOUT)
+static inline uint32_t mbedtls_ssl_conf_get_read_timeout(
+    mbedtls_ssl_config  const *conf )
+{
+    return( conf->read_timeout );
+}
+#else /* !MBEDTLS_SSL_CONF_READ_TIMEOUT */
+static inline uint32_t mbedtls_ssl_conf_get_read_timeout(
+    mbedtls_ssl_config  const *conf )
+{
+    ((void) conf);
+    return( MBEDTLS_SSL_CONF_READ_TIMEOUT );
+}
+#endif /* MBEDTLS_SSL_CONF_READ_TIMEOUT */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+#if !defined(MBEDTLS_SSL_CONF_HS_TIMEOUT_MIN)
+static inline uint32_t mbedtls_ssl_conf_get_hs_timeout_min(
+    mbedtls_ssl_config  const *conf )
+{
+    return( conf->hs_timeout_min );
+}
+#else /* !MBEDTLS_SSL_CONF_HS_TIMEOUT_MIN */
+static inline uint32_t mbedtls_ssl_conf_get_hs_timeout_min(
+    mbedtls_ssl_config  const *conf )
+{
+    ((void) conf);
+    return( MBEDTLS_SSL_CONF_HS_TIMEOUT_MIN );
+}
+#endif /* MBEDTLS_SSL_CONF_HS_TIMEOUT_MIN */
+
+#if !defined(MBEDTLS_SSL_CONF_HS_TIMEOUT_MAX)
+static inline uint32_t mbedtls_ssl_conf_get_hs_timeout_max(
+    mbedtls_ssl_config  const *conf )
+{
+    return( conf->hs_timeout_max );
+}
+#else /* !MBEDTLS_SSL_CONF_HS_TIMEOUT_MAX */
+static inline uint32_t mbedtls_ssl_conf_get_hs_timeout_max(
+    mbedtls_ssl_config  const *conf )
+{
+    ((void) conf);
+    return( MBEDTLS_SSL_CONF_HS_TIMEOUT_MAX );
+}
+#endif /* MBEDTLS_SSL_CONF_HS_TIMEOUT_MAX */
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 #if !defined(MBEDTLS_SSL_CONF_CID_LEN)
 static inline size_t mbedtls_ssl_conf_get_cid_len(