quagga: close the stdout/stderr as in other daemons

Once babald becomes a background daemon, it should not output information to
stdout, so need to close stdout.

In fact, other daemons close their stdout when they run into background, like
ospfd, isisd and bgpd, by calling daemon() which is in lib/daemon.c

Closing the stdout can fix a tee hang issue { #/usr/sbin/babeld -d |tee tmp }

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>