qcacld-3.0: Fix Wlan Tx failed when bt-coex for Rome

Current gTxChainMask1ss is 1 by default, only chain 1 can be used
by wifi when bt co-ex, if only chain0 exist or green AP switch to
1x1 mode, wifi tx will fail, connect will fail.

Add clear comment for gTxChainMask1ss to avoid confusing.
gTxChainMask1ss is only used by Rome, not by Helium and HST.

NOTE WELL: This change will have an adverse impact on products
which implicitly expect gTxChainMask1ss=1 behavior. Any such
products must update their INI file to add an explicit
"gTxChainMask1ss=1" entry.

Change-Id: I44f34f80200d057188a77f6f564a13c768fc727e
CRs-Fixed: 2426623
1 file changed