man/man7/landlock.7: Document network support

man/man7/landlock.7: Document network support

Copy over the existing wording from kernel documentation,
as it was introduced in Linux commit
51442e8d64bc (2023-10-26, "landlock: Document network support").
Landlock rules are not only about the filesystem any more
and the new wording is more appropriate.

Signed-off-by: Günther Noack <gnoack@google.com>
Cc: Mickaël Salaün <mic@digikod.net>
Cc: Tahera Fahimi <fahimitahera@gmail.com>
Cc: Tanya Agarwal <tanyaagarwal25699@gmail.com>
Cc: Daniel Burgener <dburgener@linux.microsoft.com>
Cc: <linux-security-module@vger.kernel.org>
Message-ID: <20250303195056.136777-2-gnoack@google.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>