patches: change default dhcp leasetime to 5 minutes

Related ticket: https://github.com/freifunk-berlin/firmware/issues/168
Revert "patches: fix ascii art in /etc/banner"

This reverts commit 9c8394c6ace2c17c9e9f2b4df10ca423c029f6d0.

I added my changes to the wrong patch for whatever reason.
patches: fix ascii art in /etc/banner
Merge branch 'features/dhcp_lease_time'

This merge should set the dhcp lease time for new routers to 5 minutes.