net-next: minor cleanups for bonding documentation

The section titled "Configuring Bonding for Maximum Throughput" is
actually section twelve not thirteen, and there are a couple of words
spelled incorrectly.

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Reviewed-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>