wil6210: Add support for large packets

It is possible to configure driver using mtu_max module parameter
by setting it to value in range of 68..7920 inclusive.
This is sub-optimal performance-wise in case packet is larger than 1 page.
mtu_max default value is 2228.

Change-Id: I08dad5aee31066db7e296e3ac6b965681e2008c2
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: 9a06bec9aee0ae54f175b20a8d4f5e14aef24a9f
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-testing.git


Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>