mwifiex: improve AMSDU packet aggregation for PCIe and SDIO

For PCIe, aggregate more AMSDU packets till PCIe TXBD is full.

For SDIO, aggregation was disabled for AMSDU packets because
AMSDU aggregated packet size is already 4K or 8K, SDIO Multiport
Aggregation feature didn't use to gain much previously.
Now with increased multiport aggregation buffer, we can enable
it for AMSDU packets.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>