[TIPC]: fix printk warning

gcc spits out this warning:

net/tipc/link.c: In function ‘link_retransmit_failure’:
net/tipc/link.c:1669: warning: cast from pointer to integer of different
size

More than a little bit ugly, storing integers in void*, but at least the
code is correct, unlike some of the more crufty Linux kernel code found
elsewhere.

Rather than having two casts to massage the value into u32, it's easier
just to have a single cast and use "%lu", since it's just a printk.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>