ip: Small corrections of '-tshort' option in usage

Fixed -t[short] to -ts[hort] as '-t' is related to
-timestamp option.
Signed-off-by: Vadim Kochan <vadim4j@gmail.com>

ip/ip.c

@@ -54,7 +54,7 @@ static void usage(void)
 "                    -f[amily] { inet | inet6 | ipx | dnet | bridge | link } |\n"
 "                    -4 | -6 | -I | -D | -B | -0 |\n"
 "                    -l[oops] { maximum-addr-flush-attempts } |\n"
-"                    -o[neline] | -t[imestamp] | -t[short] | -b[atch] [filename] |\n"
+"                    -o[neline] | -t[imestamp] | -ts[hort] | -b[atch] [filename] |\n"
 "                    -rc[vbuf] [size] | -n[etns] name }\n");
 	exit(-1);
 }