bonding: Remove trailing NULs from sysfs interface.

From: Wagner Ferenc <wferi@niif.hu>

Also remove trailing spaces from multivalued files.

This fixes output like for example:

$ od -c /sys/class/net/bond0/bonding/slaves
0000000   e   t   h   -   l   e   f   t       e   t   h   -   r   i   g
0000020   h   t      \n  \0
0000025

It mostly entails deleting '+1'-s after sprintf() calls: the return value
of sprintf is the number of characters printed, without the closing NUL,
ie. exactly what the sysfs interface requires.  The three multivalue
cases are different, because they also have to swallow back a trailing
space.

Signed-off-by: Ferenc Wagner <wferi@niif.hu>
Acked-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>