MFC r295836:
ifconfig(8): can't use 'name' or 'description' when creating interface with auto numbering

If one does 'ifconfig tap create name blah', it will return error because the
'name' command doesn't properly populate the request sent to ioctl(...). The
'description' command has the same bug, and is also fixed with this patch.

If one does 'ifconfig tap create mtu 9000 name blah', it DOES work, but 'tap0'
(or other sequence number) is echoed, instead of the expected 'blah'. (assuming
the name change actually succeeded)

PR: 206876
Submitted by: Marie Helene Kvello-Aune <marieheleneka@gmail.com>
Differential Revision: https://reviews.freebsd.org/D5341