Add additional size to ROOT_SIZE to allow netflow data to be collected without

Add additional size to ROOT_SIZE to allow netflow data to be collected without
running out of room.  Our initial trials on the public pl with 3GB root
partitions resulted in out of space errors, and lost netflow logs.

A preferable solution might be to have an independent partition, or to have a
reserved space in the /vserver partition, but adding a new parition is too
large a change too soon prior to relase of 4.2. And, putting non-slice data
into /vserver seems inappropriate design.