Merge pull request #6667 from kpayson64/ruby_eventfd_bug

src/ruby/ext/grpc/rb_call.c

src/ruby/ext/grpc/rb_completion_queue.c

src/ruby/ext/grpc/rb_grpc.c

src/ruby/ext/grpc/rb_server.c

src/ruby/lib/grpc/generic/active_call.rb

src/ruby/lib/grpc/generic/bidi_call.rb

src/ruby/lib/grpc/generic/rpc_server.rb