srv6-mobile: Update the document

srv6-mobile: Update the document

Updating the document of srv6-mobile plugin code integrated into stable/2001. The reason of this patch just only for the document is that the latest commit to master was reverted by the release master for some reason. The commit included not only the code for new feature, but also the updated document for the already merged code into stable/2001. The previous doc is work-in-progress status in terms of its CLI and features. It seems there is some confusion on this patch is trying to update the document of outside feature of stable/2001 which is not true. This patch exactly reflects the correct information of srv6-mobile plugin within the extent of stable/2001.

Type: docs

Signed-off-by: Satoru Matsushima <satoru.matsushima@gmail.com>
Change-Id: I376386ef6fc9584ab945db7358e3c4a698471e9b
Signed-off-by: Satoru Matsushima <satoru.matsushima@gmail.com>