Cygwin: tcp: fix IPPROTO_TCP option handling

- Drop definitions from <cygwin/sockets.h>
- Drop options only available on BSD
- Fix value of TCP_MAXSEG.  It was still defined as the BSD value
  while WinSock uses another value
- Handle the fact that TCP_MAXSEG is a R/O value in WinSock

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_socket_inet.cc

@@ -23,6 +23,7 @@
 #endif
 #include <w32api/ws2tcpip.h>
 #include <w32api/mswsock.h>
+#include <netinet/tcp.h>
 #include <unistd.h>
 #include <asm/byteorder.h>
 #include <sys/socket.h>
@@ -1682,6 +1683,20 @@ fhandler_socket_inet::setsockopt (int level, int optname, const void *optval,
       }
     default:
       break;
+
+    case IPPROTO_TCP:
+      switch (optname)
+	{
+	case TCP_MAXSEG:
+	  /* Winsock doesn't support setting TCP_MAXSEG, only requesting it
+	     via getsockopt.  Make this a no-op. */
+	  ignore = true;
+	  break;
+
+	default:
+	  break;
+	}
+      break;
     }
 
   /* Call Winsock setsockopt (or not) */