Create virtual interfaces upfront if specified on the command line

Create virtual interfaces upfront if specified on the command line

In cases like `sh /etc/netstart pair1 pair2', one of hostname.pair{1,2}
will contain a "patch pair{2,1}" command which expects the other interface
to exist.

If none exist, this would fail and netstart had to be run separately or
"patch"ed interface had to be manually created before.

There are other use cases where interfaces depend on each other, so before
(re)configuring an explicit list of interfaces, create all virtual ones
upfront so that a single netstart invocation will configure everything
correctly without having reflect dependencies in multiple ordered netstart
invocations.

Copy isin() from install.sub to help.

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