topology.switches: fix link discovery

fix a regression introduced by text address changes.

problem reported by Tonh o - Antonio Brasolin
patch tested and fixed by YAMADA Hideki

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>