isisd: fix loss of packets after circuit is brought up

isisd: fix loss of packets after circuit is brought up

The last parameter of THREAD_TIMER_ON() is the timeout, and we were
using circuit->fd for that. So, when a circuit was brought up, isisd
would miss all received packets on this circuit for quite a few seconds,
slowing down the convergence process.

To fix this, use the same logic we use in isis_receive() to calculate
this timeout.

This bug doesn't happen on Linux, which uses a different method to read
packets from the network.

Fixes the following ANVL tests on FreeBSD: ISIS-17.1, ISIS-18.6 (and
probably others too).

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>