MINOR: SSL: Store the ASN1 representation of client sessions.

Instead of storing the SSL_SESSION pointer directly in the struct server,
store the ASN1 representation, otherwise, session resumption is broken with
TLS 1.3, when multiple outgoing connections want to use the same session.
diff --git a/include/types/server.h b/include/types/server.h
index adedca4..d22f05a 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -274,7 +274,11 @@
 	char *sni_expr;             /* Temporary variable to store a sample expression for SNI */
 	struct {
 		SSL_CTX *ctx;
-		SSL_SESSION **reused_sess;
+		struct {
+			unsigned char *ptr;
+			int size;
+			int allocated_size;
+		} * reused_sess;
 		char *ciphers;			/* cipher suite to use if non-null */
 		int options;			/* ssl options */
 		struct tls_version_filter methods;	/* ssl methods */