at91: fix typo in network file

This closes #14474.

Signed-off-by: Hauke Mehrtens <[email protected]>

SVN-Revision: 38842

target/linux/at91/base-files/etc/config/network

@@ -16,5 +16,5 @@ config interface debug
 	option type 	none
 	option proto 	static
 	option ipaddr	172.18.0.18
-	option netmash	255.255.255.0
+	option netmask	255.255.255.0