ssl_test_common_source.c: new source file for common SSL test code

Create a new source file for code that is shared between ssl_client2.c
and ssl_server2.c, but cannot be compiled separately and instead needs
to be #include'd in each program that uses it.

This is for code that references macros or types that are defined
differently in the two programs.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 4e11cb3..a1fbca6 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -1088,6 +1088,7 @@
 
     return( mbedtls_net_send( io_ctx->net, buf, len ) );
 }
+#include "ssl_test_common_source.c"
 
 /*
  * Return authmode from string, or -1 on error