Adds max_pending_accept_reset_streams for legacy

[allan2]

Adds this missing function to the legacy client.

#90 was merged with half of #78. This PR is the other half.

[tisonkun]

Compile failed. Shall we rebase on the latest master to get the field added?

[tisonkun]

Seems the code itself is wrong. I made a patch at #119.

@allan2 Feel free to merge my commit into this patch. Or @seanmonstar can review #119 instead as I'll actively respond.

Credits are retained. My main target is moving this forward and then grpc/grpc-rust#1670.

[allan2]

@tisonkun thank you for the fix. Your #119 patch has been merged into this PR.

[czy-29]

Here you need to update the hyper dependency in Cargo.toml to 1.3.x, because hyper::client::conn::http2::Builder in 1.2.x does not have the max_pending_accept_reset_streams method. The hyper of Cargo.toml of the current master branch is still 1.2.0.