openvswitch: Add missing initialization in validate_and_copy_set_tun()

openvswitch: Add missing initialization in validate_and_copy_set_tun()

net/openvswitch/flow_netlink.c: In function ‘validate_and_copy_set_tun’:
net/openvswitch/flow_netlink.c:1749: warning: ‘err’ may be used uninitialized in this function

If ipv4_tun_from_nlattr() returns a different positive value than
OVS_TUNNEL_KEY_ATTR_GENEVE_OPTS, err will be uninitialized, and
validate_and_copy_set_tun() may return an undefined value instead of a
zero success indicator. Initialize err to zero to fix this.

Fixes: 1dd144cf5b4b47e1 ("openvswitch: Support VXLAN Group Policy extension")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>