Merge branch 'net-retire-dccp-socket'

Kuniyuki Iwashima says:

====================
net: Retire DCCP socket.

As announced by commit b144fcaf46d4 ("dccp: Print deprecation
notice."), it's time to remove DCCP socket.

The patch 2 removes net/dccp, LSM code, doc, and etc, leaving
DCCP netfilter modules.

The patch 3 unexports shared functions for DCCP, and the patch 4
renames tcp_or_dccp_get_hashinfo() to tcp_get_hashinfo().

We can do more cleanup; for example, remove IPPROTO_TCP checks in
__inet6?_check_established(), remove __module_get() for twsk,
remove timewait_sock_ops.twsk_destructor(), etc, but it will be
more of TCP stuff, so I'll defer to a later series.

v2: https://lore.kernel.org/20250409003014.19697-1-kuniyu@amazon.com
v1: https://lore.kernel.org/20250407231823.95927-1-kuniyu@amazon.com
====================

Link: https://patch.msgid.link/20250410023921.11307-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>