examples/l3fwd: fix option parsing

Fix minor, and non critical, copy and paste error in strncmp() of eth-dest
commandline argument.

Fixes: bd785f6f67 ("examples/l3fwd: make destination mac address configurable")

Signed-off-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Andrey Chilikin <andrey.chilikin@intel.com>

examples/l3fwd/main.c

@@ -2074,7 +2074,7 @@ parse_args(int argc, char **argv)
 			}
 
 			if (!strncmp(lgopts[option_index].name, CMD_LINE_OPT_ETH_DEST,
-				sizeof(CMD_LINE_OPT_CONFIG))) {
+				sizeof(CMD_LINE_OPT_ETH_DEST))) {
 					parse_eth_dest(optarg);
 			}