tipc: fix bug in socket reception function

In commit c637c103 ("tipc: resolve race
problem at unicast message reception") we introduced a time limit
for how long the function tipc_sk_eneque() would be allowed to execute
its loop. Unfortunately, the test for when this limit is passed was put
in the wrong place, resulting in a lost message when the test is true.

We fix this by moving the test to before we dequeue the next buffer
from the input queue.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>