ixgbe: avoid sleeping allocation in ixgbe_ipsec_vf_add_sa()

Change kzalloc() flags used in ixgbe_ipsec_vf_add_sa() to GFP_ATOMIC, to
avoid sleeping in IRQ context.

Dan Carpenter, with the help of Smatch, has found following issue:
The patch eda0333a: "ixgbe: add VF IPsec management" from Aug 13,
2018 (linux-next), leads to the following Smatch static checker
warning: drivers/net/ethernet/intel/ixgbe/ixgbe_ipsec.c:917 ixgbe_ipsec_vf_add_sa()
	warn: sleeping in IRQ context

The call tree that Smatch is worried about is:
ixgbe_msix_other() <- IRQ handler
-> ixgbe_msg_task()
   -> ixgbe_rcv_msg_from_vf()
      -> ixgbe_ipsec_vf_add_sa()

Fixes: eda0333a ("ixgbe: add VF IPsec management")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/intel-wired-lan/db31a0b0-4d9f-4e6b-aed8-88266eb5665c@moroto.mountain


Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>