adaptation: mark closed WASM plugins as such.

Don't try to make further calls to closed WASM plugins. Mark
them as closed in close(), so they get properly removed from
the list of plugins.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

pkg/adaptation/plugin.go

@@ -336,6 +336,7 @@ func (p *plugin) start(name, version string) (err error) {
 // close a plugin shutting down its multiplexed ttrpc connections.
 func (p *plugin) close() {
 	if p.impl.isWasm() {
+		p.closed = true
 		return
 	}