wlcore: make usage of nla_put clearer

handle errors of nla_put() inside the if(nla_put...) {}

This makes the code simpler and clearer because:
we take advantage from the fact that we have only one nla_put
in our routines (so no real need for goto label).
this avoids ugly goto forward followed by goto backward.

Signed-off-by: Yair Shapira <yair.shapira@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>