madvise.2: Add description of MADV_GUARD_INSTALL, MADV_GUARD_REMOVE

madvise.2: Add description of MADV_GUARD_INSTALL, MADV_GUARD_REMOVE

Lightweight guard region support has been added to Linux 6.13, which
adds MADV_GUARD_INSTALL and MADV_GUARD_REMOVE flags to the madvise()
system call.  Therefore, update the manpage for madvise() and describe
these operations.

Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Message-Id: <20241205104125.67518-1-lorenzo.stoakes@oracle.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>