i40e: add switch for link polling

There's been some need for controlling the periodic link polling for
debugging link issues.  This patch enables switching it off and on
through an ethtool private flag.  The link poll remains on by default,
but can be turned off with
	ethtool --set-priv-flags p261p1 LinkPolling off
and later turned back on with
	ethtool --set-priv-flags p261p1 LinkPolling on

To check the current status, use
	ethtool --show-priv-flags p261p1

Change-ID: I32e4ab654ff3eec90a06cf144899971b82d71c40
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
index 0c73404..f26dcb2 100644
--- a/drivers/net/ethernet/intel/i40e/i40e.h
+++ b/drivers/net/ethernet/intel/i40e/i40e.h
@@ -101,6 +101,7 @@
 
 /* Ethtool Private Flags */
 #define I40E_PRIV_FLAGS_NPAR_FLAG	BIT(0)
+#define I40E_PRIV_FLAGS_LINKPOLL_FLAG	BIT(1)
 
 #define I40E_NVM_VERSION_LO_SHIFT  0
 #define I40E_NVM_VERSION_LO_MASK   (0xff << I40E_NVM_VERSION_LO_SHIFT)
@@ -327,6 +328,7 @@
 #define I40E_FLAG_WB_ON_ITR_CAPABLE		BIT_ULL(35)
 #define I40E_FLAG_VEB_STATS_ENABLED		BIT_ULL(37)
 #define I40E_FLAG_MULTIPLE_TCP_UDP_RSS_PCTYPE	BIT_ULL(38)
+#define I40E_FLAG_LINK_POLLING_ENABLED		BIT_ULL(39)
 #define I40E_FLAG_VEB_MODE_ENABLED		BIT_ULL(40)
 
 	/* tracks features that get auto disabled by errors */