emulators/virtualbox-ose-kmod: Fix kernel panic on 13/14 with bridge mode by adding EPOCH support

In r560502, I added a patch to support EPOCH to VirtualBox 5. When we upgraded
to VirtualBox 6, that patch was (unintentionally) removed, making it impossible
to use bridge move without this current patch.

Approved by: jkim, madpilot
Differential Revision: https://reviews.freebsd.org/D29319