Add counter length macro

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index ab36f5d..b22db47 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2820,10 +2820,13 @@
 
         /* Remember current epoch settings for resending */
         ssl->handshake->alt_transform_out = ssl->transform_out;
-        memcpy( ssl->handshake->alt_out_ctr, ssl->cur_out_ctr, 8 );
+        memcpy( ssl->handshake->alt_out_ctr, ssl->cur_out_ctr,
+                sizeof( ssl->cur_out_ctr ) );
 
         /* Set sequence_number to zero */
-        memset( ssl->cur_out_ctr + 2, 0, 6 );
+        mbedtls_platform_zeroize( &ssl->cur_out_ctr[2],
+                                  sizeof( ssl->cur_out_ctr ) - 2 );
+
 
         /* Increment epoch */
         for( i = 2; i > 0; i-- )
@@ -2839,7 +2842,7 @@
     }
     else
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
-    memset( ssl->cur_out_ctr, 0, 8 );
+    mbedtls_platform_zeroize( ssl->cur_out_ctr, sizeof( ssl->cur_out_ctr ) );
 
     ssl->transform_out = ssl->transform_negotiate;
     ssl->session_out = ssl->session_negotiate;
@@ -3324,7 +3327,7 @@
     ssl->out_msglen  = 0;
     ssl->out_left    = 0;
     memset( ssl->out_buf, 0, out_buf_len );
-    memset( ssl->cur_out_ctr, 0, sizeof( ssl->cur_out_ctr ) );
+    mbedtls_platform_zeroize( ssl->cur_out_ctr, sizeof( ssl->cur_out_ctr ) );
     ssl->transform_out = NULL;
 
 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
@@ -5778,7 +5781,7 @@
     used += 8;
     if( used <= buf_len )
     {
-        memcpy( p, ssl->cur_out_ctr, 8 );
+        memcpy( p, ssl->cur_out_ctr, sizeof( ssl->cur_out_ctr ) );
         p += 8;
     }
 
@@ -6035,11 +6038,11 @@
     ssl->disable_datagram_packing = *p++;
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
-    if( (size_t)( end - p ) < 8 )
+    if( (size_t)( end - p ) < sizeof( ssl->cur_out_ctr ) )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
 
-    memcpy( ssl->cur_out_ctr, p, 8 );
-    p += 8;
+    memcpy( ssl->cur_out_ctr, p, sizeof( ssl->cur_out_ctr ) );
+    p += sizeof( ssl->cur_out_ctr );
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     if( (size_t)( end - p ) < 2 )