netfilter: nft_tunnel: ERSPAN_VERSION must not be null

netfilter: nft_tunnel: ERSPAN_VERSION must not be null

BugLink: https://bugs.launchpad.net/bugs/1862429
commit 9ec22d7c6c69146180577f3ad5fdf504beeaee62 upstream.

Fixes: af308b94a2a4a5 ("netfilter: nf_tables: add tunnel support")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>