support _BSD_SOURCE feature test macro

patch by Isaac Dunham. matched closely (maybe not exact) to glibc's
idea of what _BSD_SOURCE should make visible.

include/netinet/tcp.h

@@ -2,5 +2,22 @@
 #define _NETINET_TCP_H
 
 #define TCP_NODELAY 1
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#include <sys/types.h>
+#include <sys/socket.h>
+#define TCP_MAXSEG	 2
+#define TCP_CORK	 3
+#define TCP_KEEPIDLE	 4
+#define TCP_KEEPINTVL	 5
+#define TCP_KEEPCNT	 6
+#define TCP_SYNCNT	 7
+#define TCP_LINGER2	 8
+#define TCP_DEFER_ACCEPT 9
+#define TCP_WINDOW_CLAMP 10
+#define TCP_INFO	 11
+#define	TCP_QUICKACK	 12
+#define TCP_CONGESTION	 13
+#define TCP_MD5SIG	 14
+#endif
 
 #endif