emulators/virtualbox-ose-legacy: fix build emulators/virtualbox-ose-additions{,-nox11}-legacy on main: error: unknown type name 'uma_zone_t'

In file included from /wrkdirs/usr/ports/emulators/virtualbox-ose-additions-legacy/work/VirtualBox-5.2.44/src/VBox/Additions/freebsd/vboxvfs/vboxvfs_prov.c:42:
/wrkdirs/usr/ports/emulators/virtualbox-ose-additions-legacy/work/VirtualBox-5.2.44/src/VBox/Additions/freebsd/vboxvfs/vboxvfs.h:242:2: error: unknown type name 'uma_zone_t'

242 |         uma_zone_t      sf_node_pool;
    |         ^

Reported by: pkg-fallout
MFH: 2024Q3