Replace the remaining uses of vm_radix_node_page() by vm_radix_isleaf() and
vm_radix_topage().  This transformation eliminates some unnecessary
conditional branches from the inner loops of vm_radix_insert(),
vm_radix_lookup{,_ge,_le}(), and vm_radix_remove().

Simplify the control flow of vm_radix_lookup_{ge,le}().

Reviewed by:	attilio (an earlier version)
Tested by:	pho
Sponsored by:	EMC / Isilon Storage Division
Add new USB ID.

MFC after:	1 week
Submitted by:	Bruce Simpson <bms@fastmail.net>