make rump happy.
Rump doesn't have compat modules (the compat code is included in the
relevant librump*.so), so there's no module compat_50 listed in
link_set_modules, and thus ocryptodev's MODULE(...) can't "require"
it.
This fixes the problem of "built-in module compat_50 not found" when
starting up rump_allserver (or rump_server with -l rumpdev_opencrypto).
XXX This does not resolve the long-standing "crypto: unable to
XXX register devsw, error 17" message noted at line 78 of
XXX sys/rump/dev/lib/libopencrypto/opencrypto_component.c
9d7a921fe1