ifconfig: add -D option to print driver name for interface

Add -D option to add the drivername and unit number to ifconfig output
for normal display, including -a. Use ifconfig_get_orig_name() from
libifconfig to fetch the name. Note that this is the original name
for many drivers, but not for some exceptions like epair (which appends
'a' or 'b' to the unit number). epair interface pairs both display
as "epair0", etc. Make -v imply -D; might as well be fully verbose.

MFC after: 1 week
Reviewed by: zlei, kp
Differential Revision: https://reviews.freebsd.org/D42721