Add the gateway parameter in netplan

Signed-off-by: Manuel Buil <mbuil@suse.com>

tests/e2e/scripts/ipv6.sh

@@ -12,13 +12,16 @@ sysctl -w net.ipv6.conf.eth1.forwarding=0
 if [ -z "${os##*ubuntu*}" ]; then
   netplan set ethernets.eth1.accept-ra=false
   netplan set ethernets.eth1.addresses=["$ip4_addr"/24,"$ip6_addr"/64]
+  netplan set ethernets.eth1.gateway6="$ip6_addr_gw"
   netplan apply
 elif [ -z "${os##*alpine*}" ]; then
   iplink set eth1 down
   iplink set eth1 up
   ip -6 addr add "$ip6_addr"/64 dev eth1
+  ip -6 r add default via "$ip6_addr_gw"
 else
   ip -6 addr add "$ip6_addr"/64 dev eth1
+  ip -6 r add default via "$ip6_addr_gw"
 fi
 ip addr show dev eth1
-ip -6 r add default via "$ip6_addr_gw"
+ip -6 r