[MacPorts] #53546: Add IPv4 and IPv6 flag (-4, -6)

[MacPorts]

#53546: Add IPv4 and IPv6 flag (-4, -6)
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 Reporter:  l2dy         |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:
 Keywords:               |       Port:
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 Passed to curl and rsync, helpful under some circumstances:

 * one of IPv4 and IPv6 is metered.
 * one of them has better connectivity.

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Ticket URL: <https://trac.macports.org/ticket/53546>
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