ath10k: add encapsulation offloading support

Frame encapsulation from Ethernet into the IEEE 802.11 frame format
takes a considerable host CPU time on the xmit path. The firmware is
able to do this operation for us, so enable encapsulation offloading for
AP and Sta interface types to improve overall system performance.

The driver is almost ready for encapsulation offloading support. There
are only a few places where the driver assumes the frame format is IEEE
802.11 that need to be fixed.

Encapsulation offloading is currently disabled by default and the driver
utilizes mac80211 encapsulation support. To activate offloading, the
frame_mode=2 parameter should be passed during module loading.

On a QCA9563+QCA9888-based access point in bridged mode, encapsulation
offloading increases TCP 16-streams DL throughput from 365 to 396 mbps
(+8%) and UDP DL throughput from 436 to 483 mbps (+11%).

Tested-on: QCA9888 hw2.0 PCI 10.4-3.9.0.2-00131
Tested-on: QCA6174 hw3.2 PCI WLAN.RM.4.4.1-00157-QCARMSWPZ-1
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Tested-by: Oldřich Jedlička <oldium.pro@gmail.com> # TP-Link Archer C7 v4 & v5 (QCA9563 + QCA9880)
Tested-by: Edward Matijevic <motolav@gmail.com> # TP-Link Archer C2600 (IPQ8064 + QCA9980 10.4.1.00030-1)
Tested-by: Edward Matijevic <motolav@gmail.com> # QCA9377 PCI in Sta mode
Tested-by: Zhijun You <hujy652@gmail.com> # NETGEAR R7800 (QCA9984 10.4-3.9.0.2-00159)
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220516032519.29831-5-ryazanov.s.a@gmail.com