Replace NEKit dependency with reduced subset

GlassVPN/zhuhaow-NEKit/Socket/AdapterSocket/Factory/AdapterFactory.swift

@@ -0,0 +1,35 @@
+import Foundation
+
+/// The base class of adapter factory.
+open class AdapterFactory {
+    public init() {}
+    
+    /**
+     Build an adapter.
+
+     - parameter session: The connect session.
+
+     - returns: The built adapter.
+     */
+    open func getAdapterFor(session: ConnectSession) -> AdapterSocket {
+        return getDirectAdapter()
+    }
+
+    /**
+     Helper method to get a `DirectAdapter`.
+
+     - returns: A direct adapter.
+     */
+    public func getDirectAdapter() -> AdapterSocket {
+        let adapter = DirectAdapter()
+        adapter.socket = RawSocketFactory.getRawSocket()
+        return adapter
+    }
+}
+
+/// Factory building direct adapters.
+///
+/// - note: This is needed since we need to identify direct adapter factory.
+public class DirectAdapterFactory: AdapterFactory {
+    public override init() {}
+}