dhclient: do not add 0.0.0.0 interface alias.

[melifaro]

Summary

Initially dhclient used raw IP sockets to send the DHCP/BOOTP messages.
As there was no API to set the source IP to 0.0.0.0 for the raw sockets, dhcp client assigned 0.0.0.0 ip to the interface needed to setup.
Later, around 1998, BPF support appeared, removing the need to use the 0.0.0.0 hack on the systems with BPF.
As the 0.0.0.0 assignment was done in the dhclient-script "OS-agnostic" shell hook, it took a while to remove it.
OpenBSD switched to BPF-by-default in Feb 2004.
FreeBSD merged dhclient from the OpenBSD 3.7 (May 2005). After the 3.7 release, OpenBSD dropped this 0.0.0.0 hack.
FreeBSD never did that.

This change removes the initial 0.0.0.0 IPv4 address assignment from the dhclient scripts, as it serves no purpose.
It is effectively the copy of the OpenBSD change.

[melifaro]

Update dhclient as well

[eugen_grosbein.net]

I've tested the change several times including boot-time test and it just works for me using vtnet0.

[melifaro]

I will commit it on Tuesday, Mar 7, unless I get any objections.