To enable RSS hashing in the NIC, the RXCSUM.PCSD bit must be set.
By default, this is never set when Receive Checksum Offloading is
disabled - which causes problems higher up in the stack. This commit
enables this bit once the RSS initialization routine has finished.
Submitted by: Stephan de Wit
See also: https://lists.freebsd.org/pipermail/freebsd-current/2020-May/076148.html