[SPARK-3124] [SQL] Fix the assembly jar conflict

Both netty-3.2.2.Final.jar and netty-3.6.6.Final.jar are flatten into the assembly package, however, the class(NioWorker) signature difference leads to the failure in launching sparksql CLI/ThriftServer.

This is a work around solution to ignore the netty-3.2.2.Final jar while doing the assembling with sbt.