http2: add support to configure transport flow control values

[joliveirinha]

Adds to the transport configuration the capability to configure the maximum flow control values instead of using default ones. For applications that use a lot of client connections, being able to configure these values allows for better control on memory usage, particulary when connections are long-lived.

related: golang/go#20448

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from [email protected]:

Patch Set 1:

(1 comment)

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Patch Set 1:

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