support Mdm::Module::Ref object when linking vulns

[jmartin-tech]

In some legacy cases a database cache can result in a session reporting vulns with support for an Mdm::Module::Ref object. Due to serialization processes in these cases the string representation of name from the object needs to be passed to find_or_create_ref.

Verification

List the steps needed to make sure this thing works

• Start msfconsole
• Load a database module set

irb
modules.refresh_cache_from_module_files
sleep(5)
db.update_all_module_details
exit

• use exploit/windows/smb/ms08_067_netapi to generate a session
• Verify the refs table contains valid reference names not numbers

[jmartin-tech]

Testing shows this needed to account for empty refs that look to have caused imports to silently drop vulns with no references.

[bcook-r7]

I really like this, it makes it easier to read as well.

[bcook-r7]

I didn't use the exact same exploit module, but got the same side-effect. Thanks!