net,pppoe: fixup module init/exit subsequent calls

pernet data should allocated first and freed last
on module init/exit routines otherwise it's possible
to have unserialized calls to packet handling routines.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>