selftests: mptcp: diag: sort all #include

selftests: mptcp: diag: sort all #include

This file is the only one from this directory not to have all these
header inclusions sorted by type and alphabetical order.

Adapt them, to ease the reading, prevent conflicts during potential
future backport modifying these lines, and also to avoid having UAPI
header inclusions before libc ones, see [1].

Link: https://lore.kernel.org/20260120-uapi-sockaddr-v2-1-63c319111cf6@linutronix.de
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260203-net-next-mptcp-misc-feat-6-20-v1-8-31ec8bfc56d1@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>