vxlan: vxlan_rcv() callees: Move clearing of unparsed flags out

vxlan: vxlan_rcv() callees: Move clearing of unparsed flags out

In order to migrate away from the use of unparsed to detect invalid flags,
move all the code that actually clears the flags from callees directly to
vxlan_rcv().

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/2857871d929375c881b9defe378473c8200ead9b.1733412063.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>