networkd: bond add support for lacp rate

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
LacpduTransmitRate=fast

test:
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+3 (2)
MII Status: up
MII Polling Interval (ms): 0
Up Delay (ms): 0
Down Delay (ms): 0

802.3ad info
LACP rate: fast
Min links: 0
Aggregator selection policy (ad_select): stable
bond bond1 has no active aggregator

[tomegun: renamed from LacpduTransmitRate to LACPTransmitRate, manpage fixes and
dropped bond_ prefix from variables]