ixgbe: DCB, implement capabilities flags

ixgbe: DCB, implement capabilities flags

This implements dcbnl get and set capabilities ops. The
devices supported by ixgbe can be configured to run in
IEEE or CEE modes but not both.

With the DCBX set capabilities bit we add an explicit
signal that must be used to toggle between these modes.
This patch adds logic to fail the CEE command set_hw_all()
which programs the device with a CEE configuration if
the CEE caps bit is not set. Similarly, IEEE set
commands will fail if the IEEE caps bit is not set. We
allow most CEE config set commands to occur because they
do not touch the hardware until set_hw_all() is called.

The one exception to the above is the {set|get}app routines.
These must always be protected by caps bits to ensure
side effects do not corrupt the current configured mode.

By requiring the caps bit to be set correctly we can
maintain a consistent configuration in the hardware
for CEE or IEEE modes and prevent partial hardware
configurations that may occur if user space does
not send a complete IEEE or CEE configurations.

It is expected that user space will signal a DCBX mode
before programming device.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>