net: remove ax25 and amateur radio (hamradio) subsystem

net: remove ax25 and amateur radio (hamradio) subsystem

Remove the amateur radio (AX.25, NET/ROM, ROSE) protocol implementation
and all associated hamradio device drivers from the kernel tree.
This set of protocols has long been a huge bug/syzbot magnet,
and since nobody stepped up to help us deal with the influx
of the AI-generated bug reports we need to move it out of tree
to protect our sanity.

The code is moved to an out-of-tree repo:
https://github.com/linux-netdev/mod-orphan
if it's cleaned up and reworked there we can accept it back.

Minimal stub headers are kept for include/net/ax25.h (AX25_P_IP,
AX25_ADDR_LEN, ax25_address) and include/net/rose.h (ROSE_ADDR_LEN)
so that the conditional integration code in arp.c and tun.c continues
to compile and work when the out-of-tree modules are loaded.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Carlos Bilbao <carlos.bilbao@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260421021824.1293976-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>