ipneigh: add missing proxy keyword to help text

And while we're at it, add whitespace around braces and pipe symbol.
Signed-off-by: Phil Sutter <phil@nwl.cc>

ip/ipneigh.c

@@ -49,7 +49,7 @@ 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");
-	fprintf(stderr, "       ip neigh {show|flush} [ to PREFIX ] [ dev DEV ] [ nud STATE ]\n");
+	fprintf(stderr, "       ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ]\n");
 	exit(-1);
 }