Split the maximum fragment length into two - an input and output MFL

Since the server might want to have a different maximum fragment length
for the outgoing messages than the negotiated one - introduce a new way of
computing it. This commit also adds additional ssl-opt.sh tests ensuring
that the maximum fragment lengths are set as expected. 
mbedtls_ssl_get_max_frag_len() is now a deprecated function,
being an alias to mbedtls_ssl_get_output_max_frag_len(). The behaviour
of this function is the same as before.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index f1b5c37..845881f 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -3633,8 +3633,10 @@
         mbedtls_printf( "    [ Record expansion is unknown (compression) ]\n" );
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
-    mbedtls_printf( "    [ Maximum fragment length is %u ]\n",
-                    (unsigned int) mbedtls_ssl_get_max_frag_len( &ssl ) );
+    mbedtls_printf( "    [ Maximum input fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_input_max_frag_len( &ssl ) );
+    mbedtls_printf( "    [ Maximum output fragment length is %u ]\n",
+                    (unsigned int) mbedtls_ssl_get_output_max_frag_len( &ssl ) );
 #endif
 
 #if defined(MBEDTLS_SSL_ALPN)