ixgbe: allow to increase MTU to 3K with XDP enabled

ixgbe: allow to increase MTU to 3K with XDP enabled

Recently I encountered one case where I cannot increase the MTU size
directly from 1500 to a much bigger value with XDP enabled if the
server is equipped with IXGBE card, which happened on thousands of
servers in production environment. After applying the current patch,
we can set the maximum MTU size to 3K.

This patch follows the behavior of changing MTU as i40e/ice does.

References:
[1] commit 23b44513c3e6 ("ice: allow 3k MTU for XDP")
[2] commit 0c8493d90b6b ("i40e: add XDP support for pass and drop actions")

Fixes: fabf1bce103a ("ixgbe: Prevent unsupported configurations with XDP")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Tested-by: Chandan Kumar Rout <chandanx.rout@intel.com> (A Contingent Worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>