Merge branch 'ip_gre-flags-update'

Xin Long says:

====================
ip_gre: add support for i/o_flags update

ip_gre is using as many ip_tunnel apis as possible, newlink works
fine as gre would do it's own part in .ndo_init. But when changing
link, ip_tunnel_changelink doesn't even update i/o_flags, and also
the update of these flags would cause some other gre's properties
need to be updated or recalculated.

These two patch are to add i/o_flags update and then do adjustment
on some gre's properties according to the new i/o_flags.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>