Clearify when it's safe to set protos in SSLContext javadocs

Motivation:

We should make it clear when it safe to call the various SSLContext.set*(...) methods that configure protos to use.

Modifications:

- Enhance javadocs

Result:

Ensure people are aware that these callbacks need to be configure before the SSLContext is used to create SSL objects

Author: normanmaurer

openssl-classes/src/main/java/io/netty/internal/tcnative/SSLContext.java

@@ -587,6 +587,9 @@ private static byte[] protocolsToWireFormat(String[] protocols) {
 
     /**
      * Set next protocol for next protocol negotiation extension
+     * <p>
+     * <strong>Important: This method must only be called before any SSL object was created and used
+     * that belongs to this context. Failing to do so results in undefined behaviour.</strong>
      * @param ctx Server context to use.
      * @param nextProtos protocols in priority order
      * @param selectorFailureBehavior see {@link SSL#SSL_SELECTOR_FAILURE_NO_ADVERTISE}
@@ -600,6 +603,9 @@ public static void setNpnProtos(long ctx, String[] nextProtos, int selectorFailu
 
     /**
      * Set application layer protocol for application layer protocol negotiation extension
+     * <p>
+     * <strong>Important: This method must only be called before any SSL object was created and used
+     * that belongs to this context. Failing to do so results in undefined behaviour.</strong>
      * @param ctx Server context to use.
      * @param alpnProtos protocols in priority order
      * @param selectorFailureBehavior see {@link SSL#SSL_SELECTOR_FAILURE_NO_ADVERTISE}