bonding: fix packets_per_slave showing

There's an issue when showing the value of packets_per_slave due to
using signed integer. The value may be < 0 and thus not put through
reciprocal_value() before showing. This patch makes it use unsigned
integer when showing it.

CC: Andy Gospodarek <andy@greyhouse.net>
CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Veaceslav Falico <vfalico@redhat.com>
CC: David S. Miller <davem@davemloft.net>
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Acked-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>