When setting BT coex mode, the config was not updated for all
when there are multiple vdevs.
Modify the code to update it for all vdevs.
CRs-Fixed: 2667933
Change-Id: Ibad3adf44bef6842a12cbe7e46050b693ed474d6
Remove static from nla_policy btc_chain_mode_policy in correspondence to
the change to add policy attribute to BTC_CHAIN_MODE vendor subcommand.
Change-Id: Ie33542199d27f6b9d8ea5e0a1a063b71ecb7fd94
CRs-Fixed: 2635059