rpc: Correct the wrong payload size checking
rpc: Correct the wrong payload size checking

<...>
/* Size of message length field. Not counted in VIR_NET_MESSAGE_MAX
 * and VIR_NET_MESSAGE_INITIAL.
 */
const VIR_NET_MESSAGE_LEN_MAX = 4;
</...>

However, msg->bufferLength includes the length word. The wrong checking
was introduced by commit e914dcfd.

* src/rpc/virnetmessage.c:
  - Correct the checking in virNetMessageEncodePayloadRaw
  - Use a new variable to track the new payload length in
    virNetMessageEncodePayloadRaw

VenkatDatta/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,datto/libvirt,crobinso/libvirt,zhlcindy/libvirt-1.1.4-maintain,shugaoye/libvirt,jfehlig/libvirt,taget/libvirt,cbosdo/libvirt,andreabolognani/libvirt,rlaager/libvirt,crobinso/libvirt,andreabolognani/libvirt,elmarco/libvirt,olafhering/libvirt,rlaager/libvirt,andreabolognani/libvirt,shugaoye/libvirt,rlaager/libvirt,agx/libvirt,eskultety/libvirt,taget/libvirt,jardasgit/libvirt,shugaoye/libvirt,zhlcindy/libvirt-1.1.4-maintain,zhlcindy/libvirt-1.1.4-maintain,jardasgit/libvirt,andreabolognani/libvirt,cbosdo/libvirt,olafhering/libvirt,rlaager/libvirt,crobinso/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,nertpinx/libvirt,shugaoye/libvirt,nertpinx/libvirt,zippy2/libvirt,cbosdo/libvirt,jfehlig/libvirt,zhlcindy/libvirt-1.1.4-maintain,jfehlig/libvirt,VenkatDatta/libvirt,crobinso/libvirt,nertpinx/libvirt,agx/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,agx/libvirt,cbosdo/libvirt,elmarco/libvirt,elmarco/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,elmarco/libvirt,VenkatDatta/libvirt,agx/libvirt,agx/libvirt,libvirt/libvirt,datto/libvirt,olafhering/libvirt,taget/libvirt,zippy2/libvirt,jardasgit/libvirt,andreabolognani/libvirt,libvirt/libvirt,jardasgit/libvirt,elmarco/libvirt,VenkatDatta/libvirt,libvirt/libvirt,datto/libvirt,taget/libvirt,zhlcindy/libvirt-1.1.4-maintain,fabianfreyer/libvirt,datto/libvirt,olafhering/libvirt,eskultety/libvirt,eskultety/libvirt,eskultety/libvirt,libvirt/libvirt,eskultety/libvirt,rlaager/libvirt,taget/libvirt,shugaoye/libvirt,cbosdo/libvirt,datto/libvirt