- Made listen backlog number a define

diff --git a/library/net.c b/library/net.c
index ad2b278..e1d91e4 100644
--- a/library/net.c
+++ b/library/net.c
@@ -189,7 +189,7 @@
         return( POLARSSL_ERR_NET_BIND_FAILED );
     }
 
-    if( listen( *fd, 10 ) != 0 )
+    if( listen( *fd, POLARSSL_NET_LISTEN_BACKLOG ) != 0 )
     {
         close( *fd );
         return( POLARSSL_ERR_NET_LISTEN_FAILED );