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/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 9ff61fd..f83d014 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -260,11 +260,11 @@
 static inline uint32_t mbedtls_ssl_get_output_buflen( const mbedtls_ssl_context *ctx )
 {
 #if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
-    return (uint32_t) mbedtls_ssl_get_max_frag_len( ctx )
+    return (uint32_t) mbedtls_ssl_get_output_max_frag_len( ctx )
                + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
                + MBEDTLS_SSL_CID_OUT_LEN_MAX;
 #else
-    return (uint32_t) mbedtls_ssl_get_max_frag_len( ctx )
+    return (uint32_t) mbedtls_ssl_get_output_max_frag_len( ctx )
                + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
 #endif
 }
@@ -272,11 +272,11 @@
 static inline uint32_t mbedtls_ssl_get_input_buflen( const mbedtls_ssl_context *ctx )
 {
 #if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
-    return (uint32_t) mbedtls_ssl_get_max_frag_len( ctx )
+    return (uint32_t) mbedtls_ssl_get_input_max_frag_len( ctx )
                + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
                + MBEDTLS_SSL_CID_IN_LEN_MAX;
 #else
-    return (uint32_t) mbedtls_ssl_get_max_frag_len( ctx )
+    return (uint32_t) mbedtls_ssl_get_input_max_frag_len( ctx )
                + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
 #endif
 }