Fix parsing flow records with enterprise set.

pmacct (used by vyatta + vyos) is setting 8800 and 4300 as
enterprise in sample records which makes this module crash
without something to fix it.

If the enterprise in a record is >0 the flow will get type='unknown'
and a data property with the raw buffer data.
Merge pull request #1 from kmpm/enterprise

Fix parsing flow records with enterprise set.