SAM: Set keepalive on sockets (ticket #1573)

Also on both sides of I2CP.
BOB already does it.

apps/sam/java/src/net/i2p/sam/SAMHandlerFactory.java

@@ -46,6 +46,7 @@ class SAMHandlerFactory {
         try {
             Socket sock = s.socket();
             sock.setSoTimeout(HELLO_TIMEOUT);
+            sock.setKeepAlive(true);
             String line = DataHelper.readLine(sock.getInputStream());
             sock.setSoTimeout(0);
             if (line == null) {

apps/sam/java/src/net/i2p/sam/SAMv3StreamSession.java

@@ -263,6 +263,7 @@ class SAMv3StreamSession  extends SAMStreamSession implements SAMv3Handler.Sessi
 
 	    			// build pipes between both sockets
 	    			try {
+					clientServerSock.socket().setKeepAlive(true);
 	    				if (this.verbose)
 	    					SAMv3Handler.notifyStreamIncomingConnection(
 	    							clientServerSock, i2ps.getPeerDestination());