Disable network support if required headers cannot be found.

patch by Michael Kostylev, michael.kostylev gmail com


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@19227 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -2173,6 +2173,8 @@ if enabled network; then
         network_extralibs="-lws2_32"
         check_type ws2tcpip.h socklen_t
         check_func_headers winsock2.h closesocket
+    else
+        disable network
     fi
 fi