test: Fix helper to retrieve tail call counters
test: Fix helper to retrieve tail call counters

If the tail call counter was zero (absent) on the first node, the
helper function would simply return as if it was absent on all nodes.
This commit fixes that bug.

Fixes: e9b3844 ("test: Detect missed tail calls on upgrade/downgrade test")
Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

cilium/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium