ReceivePack: enable capabilities immediately on first line

Instead of deferring until after command parsing, enable the
capabilities after the first pkt-line has been read from the client.
This allows the server to setup the side-band-64k channel immediately.

Change-Id: I141b7fc92e983a41d3a58da8e1464a6917422b6c

org.eclipse.jgit/src/org/eclipse/jgit/transport/BaseReceivePack.java

@@ -1077,7 +1077,7 @@ public abstract class BaseReceivePack {
 	 */
 	protected void recvCommands() throws IOException {
 		PushCertificateParser certParser = getPushCertificateParser();
-		FirstLine firstLine = null;
+		boolean firstPkt = true;
 		try {
 			for (;;) {
 				String line;
@@ -1097,10 +1097,12 @@ public abstract class BaseReceivePack {
 					continue;
 				}
 
-				if (firstLine == null) {
-					firstLine = new FirstLine(line);
+				if (firstPkt) {
+					firstPkt = false;
+					FirstLine firstLine = new FirstLine(line);
 					enabledCapabilities = firstLine.getCapabilities();
 					line = firstLine.getLine();
+					enableCapabilities();
 
 					if (line.equals(GitProtocolConstants.OPTION_PUSH_CERT)) {
 						certParser.receiveHeader(pckIn, !isBiDirectionalPipe());

org.eclipse.jgit/src/org/eclipse/jgit/transport/ReceivePack.java

@@ -184,8 +184,6 @@ public class ReceivePack extends BaseReceivePack {
 			return;
 		recvCommands();
 		if (hasCommands()) {
-			enableCapabilities();
-
 			Throwable unpackError = null;
 			if (needPack()) {
 				try {