Refactor STA_HE_CTXT_CMD sending flow:

1. As the new MLD API is introduced, there are some common fields in
both the old and new APIs. The STA_HE_CTXT_CMD of the non-MLD API
has common fields with the link and mac commands of the new MLD API.
Put this common parts in functions so it can be used later by the
new MLD API.

2. The HE capability which indicates whether the NIC is ack-enabled or
not is the same for all bands. No need to take it from the specific
band which is currently in use. Take it from the low band - this
simplifies the code and doesn't require a phy_ctxt.
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230314194113.7ca960596953.Ifc3e816461abbd69c6fd87752342afcedfebc293@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>