tc-testing: update geneve options match in tunnel_key unit tests

Since iproute2 commit f72c3ad00f3b ("tc: m_tunnel_key: add options
support for vxlan"), the geneve opt output use key word "geneve_opts"
instead of "geneve_opt". To make compatibility for both old and new
iproute2, let's accept both "geneve_opt" and "geneve_opts".

Suggested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Tested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>