Add LINKDELAY to 30s

When spanning tree is enabled on the switches, the first ifup will fail
as the system won't be able to get an address (due to spanning tree does't
allow any traffic for 30s after the port goes UP)

Change-Id: I6595bdca77a4769e858939e936a7ba098c6434b5
Closes-Bug: 1324093
Merge "Add LINKDELAY to 30s" into stable/5.0