This fixes an issue when the interface being configured is the
interface through which ssh traffic is forwarded.
In a complex scenario, one needs to disable the default interface for
NAT, and use other interface for ssh. In this case, when vagrant run
`ifconfig #{ifname} inet delete`, the second ifconfig that is supposed
to restore interface settings will never be called. This might be a rare
need, but it is also strongly recommended to use `netstart` when
reconfiguring interfaces after updating `hostname.if(5)`.
The issue can be triggered when ssh connection has issues between two
`ifconfig` commands.
35d3be865f