bonding: fix primary problem for bonding

If the slave's name changed, and the bond params primary is exist, the bond should deal with the situation in two ways:

1) If the slave was the primary slave yet, clean the primary slave and reselect active slave.
2) If the slave's new name is as same as bond primary, set the slave as primary slave and reselect active slave.

If the new primary is not matching any slave in the bond, the bond should record it to params, clean the primary slave and select a new active slave.

Update bonding.txt for primary description.

v2.1->v1: Because there are too many indentions and useless verification, so rewrite
the logic for updating the primary slave.
Modify some comments for to clean the typos.

v3->v2.1: Veaceslav disagree the first patch and modify the logic for it
(bonding: update the primary slave when changing slave's name)
and resend it himself (bonding: handle slave's name change with primary_slave logic), so remove the first patch and send the last two patches.

Ding Tianhong (2):
bonding: clean the primary slave if there is no slave matching new
primary
bonding: update bonding.txt for primary description.

 Documentation/networking/bonding.txt | 3 ++-
 drivers/net/bonding/bond_options.c   | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

1.8.0