ath79: fix execute bit for 02_network on mikrotik subtarget

When creating the mikrotik subtarget, the execute bit on 02_network
was not set. Fix it.

Fixes: a66eee63368e ("ath79: add mikrotik subtarget")

Reported-by: Christopher Hill <[email protected]>
Signed-off-by: Adrian Schmutzler <[email protected]>