three gigabit ports, but some enp2611 models only have two ports
(and only one onboard PM3386.)  The current driver assumes there
are always three ports and so it doesn't work on the two-port
version of the board at all.

This patch adds a bit of logic to the enp2611 driver to limit the
number of ports to 2 if the second PM3386 isn't detected.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>