ovpn: improve 'no route to host' debug message

When debugging a 'no route to host' error it can be beneficial
to know the address of the unreachable destination.
Print it along the debugging text.

While at it, add a missing parenthesis in a different debugging
message inside ovpn_peer_endpoints_update().

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>