tests: increase hello multiplier in TI-LFA topotest

tests: increase hello multiplier in TI-LFA topotest

In this topotest, the IS-IS hello interval is set to 1 for fast
convergence. However, the current hello multiplier of 3 results in a
tight IS-IS adjacency holdtime of 3 seconds. This tight timeframe can
cause failures when the testing machine is running multiple tests at
full capacity. To improve stability under such conditions, this commit
raises the hello multiplier to 10, providing a more forgiving holdtime
and reducing the likelihood of failures.

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