MEDIUM: Add support for configurable TLS ticket keys

Until now, the TLS ticket keys couldn't have been configured and
shared between multiple instances or multiple servers running HAproxy.
The result was that if a request got a TLS ticket from one instance/server
and it hits another one afterwards, it will have to go through the full
SSL handshake and negotation.

This patch enables adding a ticket file to the bind line, which will be
used for all SSL contexts created from that bind line. We can use the
same file on all instances or servers to mitigate this issue and have
consistent TLS tickets assigned. Clients will no longer have to negotiate
every time they change the handling process.

Signed-off-by: Nenad Merdanovic <nmerdan@anine.io>
diff --git a/include/common/defaults.h b/include/common/defaults.h
index 0e37dac..3b31849 100644
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -290,4 +290,9 @@
 #ifndef OCSP_MAX_RESPONSE_TIME_SKEW
 #define OCSP_MAX_RESPONSE_TIME_SKEW 300
 #endif
+
+/* Number of TLS tickets to check, used for rotation */
+#ifndef TLS_TICKETS_NO
+#define TLS_TICKETS_NO 3
+#endif
 #endif /* _COMMON_DEFAULTS_H */