ixl(4): Fix MAC/VLAN filters accounting

ixl(4): Fix MAC/VLAN filters accounting

- Account for a filter required to enable reception of untagged frames
while registering and unregistering VLANs to avoid trying to add more
filters than HW supports

- While adding MAC/VLAN filters, pre-set matching method field in the
Admin Queue Command response buffer to expected error value to work
around an issue with some FW versions, which do not update that field if
operation fails, and be able correctly track which filters were
configured in HW.

- Remove unused IXL_MAX_FILTERS macro definition

- Update number of available MAC/VLAN filters as in newer FW versions it
was decreased by one.

- Simplify i40e_dma_mem structure

Signed-off-by: Krzysztof Galazka <krzysztof.galazka@intel.com>
Signed-off-by: Eric Joyner <erj@FreeBSD.org>
Reviewed by:	erj@
Tested by:	Gowtham Kumar Ks <gowtham.kumar.ks@intel.com>
Approved by:	re (cperciva)
Sponsored by:	Intel Corporation
Differential Revision:	https://reviews.freebsd.org/D37457

(cherry picked from commit 1d02c6b1b859e9f611bc8fe27ca3d2c16ec128c1)
(cherry picked from commit a6fa27eb5267bfaceb626d90ead84b4d9a4f5655)