gvisor-tap-vsock: Move binary to ${prefix}/libexec

`gvproxy` is a binary to forward ports for podman machine. It should not
be used as a normal user.

containers/podman#11960 (comment)

net/gvisor-tap-vsock/Portfile

@@ -4,7 +4,7 @@ PortSystem          1.0
 PortGroup           golang 1.0
 
 go.setup            github.com/containers/gvisor-tap-vsock 0.2.0 v
-revision            0
+revision            1
 
 categories          net
 license             Apache-2
@@ -27,7 +27,11 @@ build.cmd           make
 build.args          build
 
 destroot {
-    xinstall -m 0755 ${worksrcpath}/bin/gvproxy ${destroot}${prefix}/bin
+    # `gvproxy` is a binary to forward ports for podman machine. It should not
+    # be used as a normal user.
+    #
+    # https://github.com/containers/podman/issues/11960#issuecomment-943162546
+    xinstall -m 0755 ${worksrcpath}/bin/gvproxy ${destroot}${prefix}/libexec
 }
 
 # Do not check the first tags v3 and v4.