dpaa2: add support for several interface counters

Add support for IFCOUNTER_IPACKETS, IFCOUNTER_OPACKETS,
IFCOUNTER_OBYTES, IFCOUNTER_OMCASTS, IFCOUNTER_OERRORS, and
IFCOUNTER_OQDROPS.
This allows tools like systat to report the incoming and outgoing
bandwidth.

Reviewed by: dsl, Timo Völker
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D54893