com.docker.slirp: set server to a random local MAC
com.docker.slirp: set server to a random local MAC

The previous MAC we were using was highlighted by wireshark as being
an invalid source MAC.

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

djs55/vpnkit,samoht/vpnkit,djs55/vpnkit,djs55/vpnkit