Return EEXIST to 'add' when a port is already a bridge member.  This makes reconfiguration with /etc/netstart silent again.  (noticed by deraadt)
Return EEXIST to 'add' when a port is already a bridge member.  This makes
reconfiguration with /etc/netstart silent again.  (noticed by deraadt)

And do the same for 'addspan'.

ok deraadt

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars