datapath: Account for new flags args of vxlan_sock_add()

datapath: Account for new flags args of vxlan_sock_add()

The upstream commit 359a0ea
("vxlan: Add support for UDP checksums (v4 sending, v6 zero csums)")
has introduced a new flags argument to vxlan_sock_add().

OVS does not pass any flags at this point, thus specyfing 0 will be
compatible with both the old ipv6 bool and the new u32 flags argument.

Upstream: 359a0ea ("vxlan: Add support for UDP checksums (v4 sending, v6 zero csums)")
Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>