fixup! shell_commands: adapt ping6 to original-ping-like implementation

sys/shell/commands/sc_gnrc_icmpv6_echo.c

@@ -33,6 +33,9 @@
 #include "msg.h"
 #include "net/gnrc.h"
 #include "net/gnrc/icmpv6.h"
+#ifdef MODULE_GNRC_IPV6_NIB
+#include "net/gnrc/ipv6/nib/nc.h"
+#endif
 #include "net/icmpv6.h"
 #include "net/ipv6.h"
 #include "timex.h"
@@ -385,6 +388,12 @@ static void _handle_reply(_ping_data_t *data, gnrc_pktsnip_t *pkt)
     }
     ipv6_hdr = ipv6->data;
     _print_reply(data, icmpv6, &ipv6_hdr->src, ipv6_hdr->hl);
+#ifdef MODULE_GNRC_IPV6_NIB
+        /* successful ping to neighbor (NIB handles case if ipv6->src is not a
+         * neighbor) can be taken as upper-layer hint for reachability:
+         * https://tools.ietf.org/html/rfc4861#section-7.3.1 */
+    gnrc_ipv6_nib_nc_mark_reachable(&ipv6_hdr->src);
+#endif
 }
 
 static int _finish(_ping_data_t *data)