session sendHello() has bug when running as server

[hghua]

Hi, i am trying to use this amazing library as both netconf server and client.

Yet when running as server, the sent hello message is malformed: the session-id tag is inside capabilities, see session/session.go:sendHello , which is wrong, it should be outside of capabilities, see rfc6241.

Briefly as follows:

   <hello xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <capabilities>
       <capability>
         urn:ietf:params:netconf:base:1.1
       </capability>
 -     <session-id>4</session-id>    ------- wrong
     </capabilities>
 +   <session-id>4</session-id>     ------ expected
   </hello>