This includes the bump for cdevsw d_version. Otherwise, the impact on
the ABI (not KBI) is surprisingly low. The most important affected
interface is devname(3) and ttyname(3) which already correctly handle
long names (and ttyname(3) should not be affected at all).
Still, due to the d_version bump, I argue that the change is not MFC-able.
Requested by: mmacy
Reviewed by: jhb
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D18932