networkd: add support for bond options

The following bond options are supported by this patch.

MIIMonitorSec:
Specifies the frequency in milli-seconds that MII link
monitoring will occur.

UpDelaySec:
Specifies the delay time in milli-seconds to enable a link
after a link up status has been detected.

DownDelaySec:
Specifies the delay time in milli-seconds to disable a link
after a link failure has been detected.

changes:
1. Added gconf variables.
2. man page
3.

Test case:
conf file:
-----------------------
[NetDev]
Name=bond1
Kind=bond

[Bond]
Mode=active-backup
MIIMonitorSec=1s
UpDelaySec=2s
DownDelaySec=8s
----------------
test run:

cat /proc/net/bonding/bond1
Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: None
MII Status: up
MII Polling Interval (ms): 1000
Up Delay (ms): 2000
Down Delay (ms): 8000
networkd: bond add support for lacp rate

LacpduTransmitRate
option specifies the rate in which link partner to transmit
LACPDU packets in 802.3ad mode.  Possible values
slow : Request partner to transmit LACPDUs every 30 seconds
fast : Request partner to transmit LACPDUs every 1 second
The default is slow.

chages:
1. Added enum bond_lacp_rate_table
2. gperf LacpduTransmitRate

Test:
conf file:
[NetDev]
Name=bond1
Kind=bond

[Bond]
Mode=802.3ad
MIIMonitorSec=1s
UpDelaySec=2s
DownDelaySec=8s
LacpduTransmitRate=fast

test output:
$ cat /proc/net/bonding/bond1
Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: IEEE 802.3ad Dynamic link aggregation
Transmit Hash Policy: layer2 (0)
MII Status: up
MII Polling Interval (ms): 1000
Up Delay (ms): 2000
Down Delay (ms): 8000

802.3ad info
LACP rate: fast
Min links: 0
Aggregator selection policy (ad_select): stable
bond bond1 has no active aggregato
bridge: WIP wq
Merge branch 'master' into bridge