be2net: support deleting FW dump via ethtool (only for Lancer)

This patch adds support to delete an existing FW-dump in Lancer via ethtool.
Initiating a new dump is not allowed if a FW dump is already present in the
adapter. The existing dump has to be first explicitly deleted.

Signed-off-by: Kalesh AP <kalesh.purayil@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>