[squash] make reusing inet_diag sock fork+preload safe

[Eric Wong <bofh@yhbt.net>]

I'll squash this in for fork+preload safety.
Fwiw, most of the stats stuff has never seen any real-world use
to my knowledge :x   Somebody else got me to work on it but never
got around to using it, so you're probably the only guinea pig :>

diff --git a/lib/raindrops/middleware.rb b/lib/raindrops/middleware.rb
index e0781f2..a9e2ee3 100644
--- a/lib/raindrops/middleware.rb
+++ b/lib/raindrops/middleware.rb
@@ -98,8 +98,6 @@ def initialize(app, opts = {})
       tmp = Unicorn.listener_names
     end
     @nl_sock = @tcp = @unix = nil
-    defined?(Raindrops::Linux.tcp_listener_stats) and
-      @nl_sock = Raindrops::InetDiagSocket.new
 
     if tmp
       @tcp = tmp.grep(/\A.+:\d+\z/)
@@ -131,6 +129,7 @@ def stats_response  # :nodoc:
            "writing: #{@stats.writing}\n"
 
     if defined?(Raindrops::Linux.tcp_listener_stats)
+      @nl_sock ||= Raindrops::InetDiagSocket.new
       Raindrops::Linux.tcp_listener_stats(@tcp, @nl_sock).each do |addr,stats|
         body << "#{addr} active: #{stats.active}\n" \
                 "#{addr} queued: #{stats.queued}\n"