dcbnl: adding DCBX feature flags get-set

Adding a pair of set-get routines to dcbnl for setting the negotiation
flags of the various DCB features. Conforms to the CEE flavor of DCBX
The user sets these flags (enable, advertise, willing) for each feature
to be used by the DCBX engine. The 'get' routine returns which of the
features is enabled after the negotiation.

This patch is dependent on the following patches:
[net-next-2.6 PATCH 1/3] dcbnl: add support for ieee8021Qaz attributes
[net-next-2.6 PATCH 2/3] dcbnl: add appliction tlv handlers
[net-next-2.6 PATCH 3/3] net_dcb: add application notifiers

Signed-off-by: Shmulik Ravid <shmulikr@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>