When NSS ratio enabled reported by firmware, SUPPORTS_VHT_EXT_NSS_BW
is set in ath11k, meanwhile IEEE80211_VHT_EXT_NSS_BW_CAPABLE also
need to be set, otherwise it is invalid because spec in IEEE Std
802.11™‐2020 as below.

Table 9-273-Supported VHT-MCS and NSS Set subfields, it has subfield
VHT Extended NSS BW Capable, its definition is:
Indicates whether the STA is capable of interpreting the Extended NSS
BW Support subfield of the VHT Capabilities Information field.

dmesg have a message without this patch:

ieee80211 phy0: copying sband (band 1) due to VHT EXT NSS BW flag

It means mac80211 will set IEEE80211_VHT_EXT_NSS_BW_CAPABLE if ath11k not
set it in ieee80211_register_hw(). So it is better to set it in ath11k.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1
Signed-off-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211013073704.15888-1-wgong@codeaurora.org