Update generic helpdesk email address

* helpdesk@rt.linuxfoundation.org no longer works as expected
* releng@rt.linuxfoundation.org was recently added to go directly to the
  RelEng queue in RT
* Fixed missing camel case for RelEng in doc

Issue: INFRA-4466
Change-Id: I3a17973b68996e194f19c58980b5fc73712d923e
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>

docs/helpdesk.rst

@@ -22,5 +22,5 @@ these addresses depending on which project helpdesk you wish to reach:
 * Tungsten Fabric: helpdesk@tungsten.io
 
 If your project is not listed here you can send your inquiry to the Generic
-releng helpdesk channel helpdesk@rt.linuxfoundation.org along with the name
+RelEng helpdesk channel releng@rt.linuxfoundation.org along with the name
 of the project in the subject line.