net: vrf: remove skb_dst_force() after skb_dst_set()

skb_dst_set(skb, dst) installs a normal (refcounted) dst, there is no
point using skb_dst_force(skb)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>