When SRv6 is initialized on a given IS-IS area, set the administrative
enabled status to the default value defined by the YANG model.
Signed-off-by: Carmine Scarpitta <carmine.scarpitta@uniroma2.it>
Add `isis_srv6.c` and `isis_srv6.h` files needed to support SRv6 in IS-IS
(as per RFC 9352).
Signed-off-by: Carmine Scarpitta <carmine.scarpitta@uniroma2.it>