From function nud_state_a2n we can see there are more states could be used. So
update the ip neigh usage.

Signed-off-by: Hangbin Liu <redacted>
---
 ip/ipneigh.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/ip/ipneigh.c b/ip/ipneigh.c
index d76e035..c203775 100644
--- a/ip/ipneigh.c
+++ b/ip/ipneigh.c

@@ -46,9 +46,12 @@ static void usage(void) __attribute__((noreturn));
 static void usage(void)
 {
 	fprintf(stderr, "Usage: ip neigh { add | del | change | replace } { ADDR [ lladdr LLADDR ]\n"
-		        "          [ nud { permanent | noarp | stale | reachable } ]\n"
-		        "          | proxy ADDR } [ dev DEV ]\n");
+		        "                    [ nud STATE ] | proxy ADDR } [ dev DEV ]\n");
+	fprintf(stderr, "\n");
 	fprintf(stderr, "       ip neigh {show|flush} [ to PREFIX ] [ dev DEV ] [ nud STATE ]\n");
+	fprintf(stderr, "\n");
+	fprintf(stderr, "STATE := { permanent | reachable | noarp | none | stale |\n");
+	fprintf(stderr, "           incomplete | delay | probe | failed }\n");
 	exit(-1);
 }