qcacld-3.0: Incorrect phymode sent as part of peer_assoc

Incorrect phy mode sent to firmware as part of the
TDLS connection peer assoc command.

VHT phymode representation for 2G and 5G is different
and host is sending 5G VHT phymode as part of the 2G
TDLS connection peer_assoc command to firmware.

Modified phymode generation logic at WMA for TDLS
connection to populate 'WLAN_PHYMODE_11AC_VHT20_2G'
phymode.

Change-Id: I7867df7f013bc05a182e33495181a099332d1fd5
CRs-Fixed: 2719278