Override Net::LDAP sockets for Rex::Socket

To flesh out Net::LDAP integration, client connections should be
able to pivot over Meterpreter sessions and respect proxy settings
for TCP sockets.

This commit provides a basic override to the Connection class in
Net::LDAP to establish their outbound connection using our sockets
tier.

Once a proper LDAP client is written for Rex, this hack can be
dropped.

Testing:
  Has worked for years in Semper Victus' repo

TODO:
  Replace this with a real LDAP client tying into the datastore and
proper Framework context

lib/rex/proto/ldap.rb

@@ -0,0 +1,27 @@
+require 'net/ldap'
+require 'rex/socket'
+
+class Net::LDAP::Connection #:nodoc:
+  LdapVersion = 3
+  MaxSaslChallenges = 10
+
+  def initialize(server)
+    begin
+     @conn = Rex::Socket::Tcp.create(
+       'PeerHost' => server[:host],
+       'PeerPort' => server[:port],
+       'Proxies'  => server[:proxies]
+     )
+    rescue SocketError
+      raise Net::LDAP::LdapError, "No such address or other socket error."
+    rescue Errno::ECONNREFUSED
+      raise Net::LDAP::LdapError, "Server #{server[:host]} refused connection on port #{server[:port]}."
+    end
+
+    if server[:encryption]
+      setup_encryption server[:encryption]
+    end
+
+    yield self if block_given?
+  end
+end