net: eth_legacy - fix build CMD_PCAP

Fix typo which would cause a build error.

Fixes: 3eaac630 ("net: introduce packet capture support")
Signed-off-by: NJorge Ramirez-Ortiz <jorge@foundries.io>

net/eth_legacy.c

@@ -365,7 +365,7 @@ int eth_send(void *packet, int length)
 	ret = eth_current->send(eth_current, packet, length);
 #if defined(CONFIG_CMD_PCAP)
 	if (ret >= 0)
-		pcap_post(packet, lengeth, true);
+		pcap_post(packet, length, true);
 #endif
 	return ret;
 }