iperf2: fix sha256 hash for modified tarball
iperf2: fix sha256 hash for modified tarball

Upstream reuploaded the iperf2 tarball shortly after release:
https://sourceforge.net/p/iperf2/tickets/132/?limit=25#1696

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs