bonding: cleanup module option descriptions

Weiping Pan noticed that the module option description for
xmit_hash_policy was incorrect and was nice enough to post a patch to
fix it.  The text was correct, but created a line over 80 characters and
I would rather not add those.  I realized I could take a few minutes and
clean up all the descriptions and things would look much better.  This
is the result.

Based on patch from Weiping Pan <panweiping3@gmail.com>.

Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
CC: Weiping Pan <panweiping3@gmail.com>
Reviewed-by: Weiping Pan <panweiping3@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>