Add sysctls to control device side USB identifiers. This makes it
possible to change string and numeric vendor and product identifiers,
as well as anything else there might be to change for a particular
device side template, eg the MAC address.
Reviewed by: hselasky@
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D13920