support max_pages_limit

[hanwen]

commit 78eeae60bb5a978eae4c3ce705c58189b762a24b
Author: Joanne Koong joannelkoong@gmail.com
Date: Wed Sep 25 17:49:56 2024 -0700

Initialize session buffer size to value set by sysctl

This commit adds support for this on the libfuse side to set
the fuse session buffer to take into account the max pages
limit set in /proc/sys/fs/fuse/max_pages_limit. If this
sysctl does not exist (eg older kernels), it will default to
old behavior (using FUSE_MAX_MAX_PAGES (256) as the max pages
limit). This allows for things like bigger write buffers per
request.