Adding some files that was accidentally removed
(instead of moved) in cleanup part 2.

Remove support for historic Linux kernels,
merge krt-iface, krt-set and krt-scan stub headers.

OS-dependent functions renamed to be more consistent,
prepared to merge krt-set and krt-scan headers.

Name changes:

struct krt_if_params -> struct kif_params
struct krt_if_status -> struct kif_status
struct krt_set/scan_params -> struct krt_params
struct krt_set/scan_status -> struct krt_status

krt_if_params_same -> kif_sys_reconfigure
krt_if_copy_params -> kif_sys_copy_config
krt_set/scan_params_same -> krt_sys_reconfigure
krt_set/scan_copy_params -> krt_sys_copy_config

krt_if_scan -> kif_do_scan
krt_set_notify -> krt_do_notify
krt_scan_fire -> krt_do_scan

krt_if_ -> kif_sys_
krt_scan_ -> krt_sys_
krt_set_ -> krt_sys_

Thanks to Howden Nick for the bugreport.

Based on the patch from Alexander V. Chernikov.
Extended to support almost all protocols.
Uses 'protocol bgp NAME from TEMPLATE { ... }' syntax.

Thanks to Alexander V. Chernikov for the patch.

Adds option -u and -g to specify user and group.
When different user (than root) is specified,
linux capabilities CAP_NET_* are kept.

Mainly changes IA_UNNUMBERED to IA_PEER and adds IA_HOST. Also do not
show broadcast addr in show interfaces. Nobody cares for that.

Also changes some symbol names (IFF_ADMIN_DOWN -> IFF_SHUTDOWN,
IFF_LINK_UP -> IFF_ADMIN_UP).

Hostcache is a structure for monitoring changes in a routing table that
is used for routes with dynamic/recursive next hops. This is needed for
proper iBGP next hop handling.

In usual configuration, such export is already restricted
with the aid of the direct protocol but there are some
races that can circumvent it. This makes it harder to
break kernel device routes. Also adds an option to
disable this restriction.

- BSD kernel syncer is now self-conscious and can learn alien routes
- important bugfix in BSD kernel syncer (crash after protocol restart)
- many minor changes and bugfixes in kernel syncers and neighbor cache
- direct protocol does not generate host and link local routes
- min_scope check is removed, all routes have SCOPE_UNIVERSE by default
- also fixes some remaining compiler warnings

Finally, it is working.