wlcore: use dynamic keep-alive template ids

Currently, all the (station) roles use the same
keep-alive template id (0). However, the klv
template ids shouldn't be shared by different
roles.

Implement a simple klv_templates bitmap, and let
each role allocate its own klv template id on
role initialization.

[Arik - remove invalidation of KLV template when getting into "idle".
This is already handled in unjoin]

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <luca@coelho.fi>