Import lwIP contrib rep

... from http://git.savannah.gnu.org/cgit/lwip/lwip-contrib.git/ into contrib/ subdir, STABLE-2_1_0_RELEASE tag
lwIP contrib is now officially frozen
TODO: Fix build

contrib/ports/win32/check/sys/time.h

@@ -0,0 +1,12 @@
+#ifndef LWIP_SYS__TIME_H
+#define LWIP_SYS__TIME_H
+
+#include <stdlib.h> /* time_t */
+
+struct timeval {
+  time_t    tv_sec;         /* seconds */
+  long    tv_usec;        /* and microseconds */
+};
+int gettimeofday(struct timeval* tp, void* tzp);
+
+#endif