erspan: set erspan_ver to 1 by default when adding an erspan dev

After erspan_ver is introudced, if erspan_ver is not set in iproute, its
value will be left 0 by default. Since Commit 02f99df1 ("erspan: fix
invalid erspan version."), it has broken the traffic due to the version
check in erspan_xmit if users are not aware of 'erspan_ver' param, like
using an old version of iproute.

To fix this compatibility problem, it sets erspan_ver to 1 by default
when adding an erspan dev in erspan_setup. Note that we can't do it in
ipgre_netlink_parms, as this function is also used by ipgre_changelink.

Fixes: 02f99df1

 ("erspan: fix invalid erspan version.")
Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>