Actually change the USB_PORT_ROOT_RESET_DELAY definition as stated in
the r241987 commit message, instead of having users locally overriding
the value using tunables in /boot/loader.conf .

Found by:	Adam Parco
Discussed with:	Nick Hibma


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273456 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f