vty: allow 0 as conn-timeout to disable it

VTY command to disable conn-timeout again, after it has been enabled.
conn-timeout was introduced in [1].

[1] Change-Id I18886052e090466f73829133c24f011806cc1fe0.
Change-Id: I7dee7dafaaf4bb93fd692ea06b52b9e012beac6d
1 file changed