wlcore: configure rates in multiple cases

The current code configures the peer caps only on BSS_CHANGED_HT
notification. However, we have to configure the peer caps
(and rates) even when HT is not enabled. Otherwise, the fw
continues working with low rates.

Configure the peer caps when sta_exists is true (i.e. when
we extracted the sta rates, e.g. on association).

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>