net_qdisc_nfs_low: Abort on error

Currently the script continues on errors. This has the problem, that
the relevant first error message might be followed by less relevant
following error messages:

/usr/sbin/net_qdisc_nfs_low: line 3: /etc/local/mxhost.conf: Permission denied
Cannot find device "root"
Unknown qdisc "10:1", hence option "handle" is unparsable
Unknown qdisc "10:2", hence option "handle" is unparsable
Unknown qdisc "10:3", hence option "handle" is unparsable
Unknown filter "10:", hence option "handle" is unparsable
Unknown filter "10:", hence option "handle" is unparsable
Unknown filter "10:", hence option "handle" is unparsable
Unknown filter "10:", hence option "handle" is unparsable

buczek@dose:~$ net_qdisc_nfs_low status
/usr/sbin/net_qdisc_nfs_low: line 3: /etc/local/mxhost.conf: Permission denied
Command line is not complete. Try option "help"
Command line is not complete. Try option "help"

Set the shell to -e so that we get only the first message and are sure
we exit with a non-zero exit status on errors.

net_qdisc_nfs_low/net_qdisc_nfs_low

@@ -1,5 +1,7 @@
 #! /bin/bash
 
+set -e
+
 . /etc/local/mxhost.conf
 
 case "$1" in