This fixes the logic that decides if a node name is valid to use the
same length restrictions that are used in drmDeviceAlloc, which expects
node names to conform to a specific naming scheme (On OSes except
OpenBSD this means `/dev/dri/renderD123`). This addresses the problem of
node names that are longer than expected, while still allowing symlinks
to work.

I've also applied the same fix to the OpenBSD path, while bringing the
check that `snprintf` didn't error from OpenBSD to the main path.

Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Tested-by: Mark Janes <markjanes@swizzler.org>
Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>