com.docker.slirp: add the --dns argument
com.docker.slirp: add the --dns argument

Both frontends now support this argument, previously it was Windows-only.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit