netconsole: move local_port / remote_port from struct netpoll to netconsole_target

The source and destination UDP ports live in struct netpoll but are
netconsole configuration. No other netpoll user (bonding, team, vlan,
bridge, macvlan, dsa) touches np->local_port or np->remote_port; they
only use the netpoll TX/forwarding path. Only netconsole's UDP framing
and its configfs/cmdline interface read these fields.

Move both into struct netconsole_target and convert the three helpers
that read them - push_udp(), netconsole_print_banner() and
netconsole_parser_cmdline() - to take the netconsole_target. The
configfs show/store handlers already have the target in hand.

No functional change; the local_port / remote_port sysfs attributes are
unchanged.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260710-netconsole_move_more-v3-8-6f63f76b28bc@debian.org
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>