selftests: traceroute: Reword comment

selftests: traceroute: Reword comment

Both of the addresses are configured as primary addresses, but the
kernel is expected to choose 10.0.1.1/24 as the source IP of the ICMP
error message since it is on the same subnet as the destination IP of
the message (10.0.1.3/24). Reword the comment to reflect that.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20250908073238.119240-7-idosch@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>