iwlwifi: mvm: set seqno also when no keys are set

In an open BSS, after suspend/resume, we don't set the last seqno
because the iwl_mvm_setup_connection_keep() returns too early.  This
happens because the check to see if we have any keys was returning
immediately, without setting seqno and seqno_valid.  Fix this.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>