dpnaa2: announce transmit checksum support

Let the network stack know that the NIC supports checksum offloading
for the IPv4 header checksum and the TCP and UDP transport checksum.
This avoids the computation in software and therefore provides the
expected performance gain.

PR: 292006
Reviewed by: dsl, Timo Völker
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D54809