When the kernel is started using ip=dhcp, we want a way to be able to run
the udhcp client within busybox and not reset the interface.

When using the '-D' option to udhcpc, the defconfig script will be skipped
allowing the refresh without changing the network settings.

Also provide an initscript that can be used to detect ip=dhcp on the
kernel command line, if detected it will refresh the lease and set the
proper resolve.conf and related files, but not reset the interface.

Original code in Wind River Linux by Greg Moffatt <greg.moffat@windriver.com>

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>