wifi: iwlwifi: mvm: fix getting LDPC/STBC support

Use flags field from struct ieee80211_tx_info in order to get
LDPC/STBC support. The rate parameter, used originally, is 16
bits only and does not have details of LDPC/STBC support.

Signed-off-by: Mukesh Sisodiya <mukesh.sisodiya@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230612184434.5a8856739b11.I6af4a55b22ed856f484ba77f87723dceec4904f2@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>