Add rescue to warn of exceptions when receiving invalid/mangled sflow packets

[dejongm]

This is to fix an issue where Logstash drops the UDP listener when receiving an invalid/mangled sflow packet and closes with the following exception:

Exception in inputworker {"exception"=>#, "backtrace"=>["/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/io.rb:314:in read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/io.rb:333:inaccumulate_big_endian_bits'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/io.rb:322:in read_big_endian_bits'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/io.rb:295:inreadbits'", "(eval):30:in read_and_return_value'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/base_primitive.rb:129:indo_read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/struct.rb:139:in do_read'", "org/jruby/RubyArray.java:1613:ineach'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/struct.rb:139:in do_read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/array.rb:322:indo_read'", "org/jruby/RubyArray.java:1613:in each'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/array.rb:322:indo_read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/struct.rb:139:in do_read'", "org/jruby/RubyArray.java:1613:ineach'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/struct.rb:139:in do_read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/base.rb:147:inread'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/base.rb:254:in start_read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/base.rb:145:inread'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/bindata-2.4.0/lib/bindata/base.rb:21:in read'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/logstash-codec-sflow-2.0.0/lib/logstash/codecs/sflow.rb:105:indecode'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/logstash-input-udp-3.1.0/lib/logstash/inputs/udp.rb:118:in inputworker'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/logstash-input-udp-3.1.0/lib/logstash/inputs/udp.rb:89:inudp_listener'"]}

[ashangit]

Thanks @dejongm for this patch