This is a flag to be used to disable >1 antenna support, even if
the radio supports it.
Also populate sku_cap_11n_enable, which indicates HT is available.
It's a no-op right now; it's one of the requirements for properly
configuring HT support and transmit/receive antenna configurations.
Obtained from: OpenBSD (at a6e25c727a2214219715b51ba6af2221d7e0d674, 22-Oct-2021)