bgpd: Send Hard Reset Notification for BGP_NOTIFY_CEASE_ADMIN_RESET

bgpd: Send Hard Reset Notification for BGP_NOTIFY_CEASE_ADMIN_RESET

`clear bgp neighbor` should send Hard Reset and graceful restart should be
activated. Let's make this adjustable.

https://datatracker.ietf.org/doc/html/rfc8538#section-5.1

   +-------+------------------------------------+----------------------+
   | Value |                Name                |  Suggested Behavior  |
   +-------+------------------------------------+----------------------+
   |   1   | Maximum Number of Prefixes Reached |      Hard Reset      |
   |   2   |      Administrative Shutdown       |      Hard Reset      |
   |   3   |         Peer De-configured         |      Hard Reset      |
   |   4   |        Administrative Reset        | Provide user control |
   |   5   |        Connection Rejected         |    Graceful Cease    |
   |   6   |     Other Configuration Change     |    Graceful Cease    |
   |   7   |  Connection Collision Resolution   |    Graceful Cease    |
   |   8   |          Out of Resources          |    Graceful Cease    |
   |   9   |             Hard Reset             |      Hard Reset      |
   +-------+------------------------------------+----------------------+

Enabled by default.

Co-authored-by: Biswajit Sadhu <biswajit.sadhu@gmail.com>
Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>