PR 15662 is already applied to -current, however i don't think it
	is doing the right thing.  kernel shouldn't be removing routes
	without user knowing it (for RTF_DYNAMIC/CLONED case, it should be
	okay, however, the code doe snot check it).  user can alter ia_ifa
	manually, therefore i guess we shouldn't even be updating ia_ifa.

	you can see panic with the following because of the change.
>               ifconfig ex0 192.168.0.69
>               ifconfig ex0 192.168.0.20 alias
>               ifconfig ex0 192.168.0.20

itojun