don't use socat for port forwarding

use goroutines to copy the data from the stream to the TCP
connection, and viceversa, removing the socat dependency.

Quoting Lantao Liu, the logic is as follow:

When one side (either pod side or user side) of portforward
is closed, we should stop port forwarding.

When one side is closed, the io.Copy use that side as source will close,
but the io.Copy use that side as dest won't.

Signed-off-by: Antonio Ojea <antonio.ojea.garcia@gmail.com>

.github/workflows/ci.yml

@@ -107,8 +107,7 @@ jobs:
           sudo apt-get install -y \
             btrfs-tools \
             libseccomp2 \
-            libseccomp-dev \
-            socat
+            libseccomp-dev
           make install.deps
         working-directory: ${{github.workspace}}/src/github.com/containerd/cri