Fix unprotected debugs to warns and fix

Fix unprotected debugs to warns and fix

In the case of a route replace failing we
saw two issues with the logging:

1) The route replace was a debug instead of a warn
  -> In this case change code to zlog_warn
2) The buf in the route replace was not being initialized
because buf initialization was protected by a debug check.
  -> In this case move the buf initialization to inside
the failure case.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>
Reviewed-by: Vivek Venkatraman <vivek@cumulusnetworks.com>