buildvm-s390x-21: Fix up mac address

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

inventory/host_vars/buildvm-s390x-21.s390.fedoraproject.org

@@ -6,9 +6,7 @@ dns_search2: "fedoraproject.org"
 eth0_ipv4: 10.16.0.32
 eth0_ipv4_gw: 10.16.0.254
 eth0_ipv4_nm: 24
-eth0_mac: "{{ mac0 }}"
 has_ipv4: yes
-mac0: 52:54:00:42:6d:23
 network_connections:
   - autoconnect: yes
     ip:
@@ -22,7 +20,7 @@ network_connections:
         - "{{ dns_search1 }}"
         - "{{ dns_search2 }}"
       gateway4: "{{ eth0_ipv4_gw }}"
-    mac: "{{ eth0_mac }}"
+    mac: "{{ ansible_default_ipv4.macaddress }}"
     name: eth0
     state: up
     type: ethernet