docs don't show bond parameters

[Mark Shuttleworth]

It took me a while to figure out that a bond needed a 'parameters' stanza for things like mode. The error on generate wasn't helpful:

$ sudo netplan generate
Error in network definition //etc/netplan/01-netcfg.yaml line 21 column 6: unknown key mode

Given the nature of the bond stanza as a mapping anyway, is the 'parameters' element actually necessary? Why not just add things like mode to the bond interface, like this:

  bonds:
    bond-conntrack:
      interfaces: [enp5s0, enp6s0]
      addresses: [192.168.254.3/24]
      mode: balance-rr
      mii-monitor-interval: 1

Alternatively, if there is a good reason to keep the 'parameters' section, please show that in the examples :)