Change switch to if (#10880)

Motivation:
switch is used when we have a good amount of cases because switch is faster than if-else. However, we're using only 1 case in switch which can affect performance.

Modification:
Changed switch to if.

Result:
Good code.

codec-http/src/main/java/io/netty/handler/codec/http/DefaultHttpHeaders.java

@@ -489,12 +489,10 @@ public class DefaultHttpHeaders extends HttpHeaders {
                     }
                     break;
                 case 1:
-                    switch (character) {
+                    if (character == '\n') {
-                        case '\n':
+                        return 2;
-                            return 2;
-                        default:
-                            throw new IllegalArgumentException("only '\\n' is allowed after '\\r': " + seq);
                     }
+                    throw new IllegalArgumentException("only '\\n' is allowed after '\\r': " + seq);
                 case 2:
                     switch (character) {
                         case '\t':