bonding: convert mode setting to use the new option API

This patch makes the bond's mode setting use the new option API and
adds support for dependency printing which relies on having an entry for
the mode option in the bond_opts[] array.
Also add the ability to print the mode name when mode dependency fails
and fix some trivial/style errors.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>