topotests: fix default BFD peer shutdown state

topotests: fix default BFD peer shutdown state

The commit `bfdd: simplify and remove duplicated code` fixed a problem
that was causing the protocol configuration to override the user
configuration.

In this test case: the peer was configured to be disabled (default is
`shutdown`) and the test was expecting it to get activated (`no shutdown`)
when the protocol converged. I changed the peer default state to
`no shutdown`, however another way to get the same effect is to
configure the protocol to use a profile or don't configure a peer at all
(and use the defaults).

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>