bgpd: add locator name in sid notify messages

bgpd: add locator name in sid notify messages

In the near future, some daemons may only register SIDs. This may be
the case for the pathd daemon when creating SRv6 binding SIDs.

When a locator is getting deleted at ZEBRA level, the daemon may have
an easy way to find out the SIds to unregister to.

This commit proposes to add the locator name to the SID_SRV6_NOTIFY
message whenever possible. Only case when an allocation failure happens,
the locator will not be present. In all other places, the notify API
at procol levels has the locator name extra-parameter.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Signed-off-by: Carmine Scarpitta <cscarpit@cisco.com>