1.27:
Use get_if_var() to retrieve interface specific values of dhclient_flags
and background_dhclient. This allows interfaces who's names are not
valid parts of shell variables and shortens the code.
1.31:
When the state of the interface changes rapidly enough there is a race
where dhclient is in the process of exiting due to the link going down
when the link coming up causes devd to try and start a new one. This
results is the link being up, but no dhclient running.
Work around this race by checking a second time after a one second delay
before refusing to start a dhclient instance due to one already being
running.
7f99930208