[BUILD] compilation of haproxy-1.4-dev2 on FreeBSD

Please consider the following patches. They are required to
compile haproxy-1.4-dev2 on FreeBSD.

Summary:
1) include <sys/types.h> before <netinet/tcp.h>
2) Use IPPROTO_TCP instead of SOL_TCP
(they are both defined as 6, TCP protocol number)

diff --git a/src/backend.c b/src/backend.c
index 7a6b7b8..05ce1ef 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -17,6 +17,7 @@
 #include <syslog.h>
 #include <string.h>
 #include <ctype.h>
+#include <sys/types.h>
 
 #include <common/compat.h>
 #include <common/config.h>