vti: remove duplicated code to fix a memory leak

vti module allocates dev->tstats twice: in vti_fb_tunnel_init()
and in vti_tunnel_init(), this lead to a memory leak of
dev->tstats.

Just remove the duplicated operations in vti_fb_tunnel_init().

(candidate for -stable)

Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Saurabh Mohan <saurabh.mohan@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>