send router solicitations every 4 seconds

See bug #53973

Signed-off-by: Simon Goldschmidt <goldsimon@gmx.de>

src/include/lwip/nd6.h

@@ -58,6 +58,11 @@ extern "C" {
 /** 1 second period */
 #define ND6_TMR_INTERVAL 1000
 
+/** Router solicitations are sent in 4 second intervals (see RFC 4861, ch. 6.3.7) */
+#ifndef ND6_RTR_SOLICITATION_INTERVAL
+#define ND6_RTR_SOLICITATION_INTERVAL  4000
+#endif
+
 struct pbuf;
 struct netif;