Move calls to virTypedParamsSerialize earlier in the event dispatch
functions so that we don't have to call 'xdr_free' afterwards.

This is possible as virTypedParamsSerialize cleans up after itself if it
fails.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
ACKed-by: NEric Blake <eblake@redhat.com>