net/sched: act_ife: Unexport ife_tlv_meta_encode

As the function ife_tlv_meta_encode is not used by any other module,
unexport it and make it static for the act_ife module.

Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>