net-mgmt/arpwatch: Update to 3.1. Remove ETHERCODES option and add
some pkg-message explaining how to use the new update-ethercodes
script. Remove obsolete patches. Changes since 3.0:

• Fix the FreeBSD rc.d script to handle interface names with . in them. Reported by Daniel Duerr.

• Add python 2 compatibility to massagevendor (for pfsense <= 2.4.4).

• Stop distributing ethercodes.dat and add update-ethercodes.sh to download and generate it.