emulators/open-vm-kmod: unbreak build on recent -CURRENT after 797020a76406a8e7a4afbd3706884b58a6e4b4ec (+)

In commit 797020a76406a8e7a4afbd3706884b58a6e4b4ec vm_page_lock() was retired
and only one compat shim now is available -- vm_page_tryxbusy() as
it used in linux compatibility layer.

Adjust code by redefine macros under __FreeBSD_version check

PR: 287811
Approved by: garga