Only rx_usec and tx_usec options for ethtool -C are settable as those
are the only settings that make sense to HW.  Adds driver reporting of
intr coalescing timer value in usec units rather than HW units.
Signed-off-by: NVasanthy Kolluri <vkolluri@cisco.com>
Signed-off-by: NScott Feldman <scofeldm@cisco.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>