Add NETIF_F_HW_CSUM to netdev_features.h as needed by a driver.
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D34233
(cherry picked from commit 85d61bd872)
Add netdev_features.h as a spearate file from the future netdevice.h
implementation to avoid include problems with a future skbuff.h.
Sponsored by: The FreeBSD Foundation
(cherry picked from commit 490f9d8f0e)