fabric: fix check for peer switch

roles/fabric/templates/bond.intf.j2

@@ -12,7 +12,7 @@ iface {{ bond.name }}
 {% endif %}
 
 {#- If the peer shares a bond with the same name, generate a clag-id for it unless the bonded link is to peer itself. #}
-{% if peer %}
+{% if peer is defined %}
 {% set peer_members = hostvars[peer].interfaces
     | selectattr('lag') | selectattr('lag.name', '==', bond.name) %}
 {% if peer_members | iface_peer | reject('eq', inventory_hostname) %}