Add some efficiency improvements

lib/msf/core/post/linux/system.rb

@@ -110,11 +110,9 @@ module System
   def get_listening_services(portsonly = false)
     services = {}
     begin
-      full = cmd_exec('netstat -tulpn')
+      full = cmd_exec('netstat -tulpn').to_s
       raise "You must be root to get listening ports" if full.include? '(No info could be read'
-      lines = full.split("\n").size
-      cmd = "netstat -tulpn | tail -n #{lines - 2}"
-      full = cmd_exec(cmd)
+      full = full[2..-1]
       full.delete!(':') # Only happens when getting services
 
       if portsonly