net/mlx4_en: Advertize encapsulation offloads features only when VXLAN tunnel is set

net/mlx4_en: Advertize encapsulation offloads features only when VXLAN tunnel is set

[ Upstream commit f4a1edd56120249198073aa4a373b77e3700ac8f ]

Currenly we only support Large-Send and TX checksum offloads for
encapsulated traffic of type VXLAN. We must make sure to advertize
these offloads up to the stack only when VXLAN tunnel is set.

Failing to do so, would mislead the the networking stack to assume
that the driver can offload the internal TX checksum for GRE packets
and other buggy schemes.

Reported-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>