client: restrict bufferlist to total write size

client: restrict bufferlist to total write size

In linux, systems calls like write() anyways don't allow writes > 2GiB,
the total write size passed to the Client::_write is clamped to INT_MAX
but bufferlist is not handled. This edge case is patched here.

bug that arises due to buffer list beyond INT_MAX stalls async i/o due to:
unknown file: Failure
C++ exception with description "End of buffer [buffer:2]" thrown in the test body.
2024-05-28T16:17:06.854+0530 7f9a5d24c9c0  2 client.4311 unmount
2024-05-28T16:17:06.854+0530 7f9a5d24c9c0  2 client.4311 unmounting

which results in disconnected inode and cap leaks:
2024-05-28T16:17:11.855+0530 7f9a5d24c9c0  1 client.4311 dump_inode: DISCONNECTED inode 0x10000000001 #0x10000000001 ref 3 0x10000000001.head(faked_ino=0 nref=3 ll_ref=0 cap_refs={4=0,1024=1,4096=1,8192=2} open={3=0} mode=100666 size=0/4294967296 nlink=1 btime=2024-05-28T16:17:03.387546+0530 mtime=2024-05-28T16:17:03.387546+0530 ctime=2024-05-28T16:17:03.387546+0530 change_attr=0 caps=pAsxLsXsxFsxcrwb(0=pAsxLsXsxFsxcrwb) objectset[0x10000000001 ts 0/0 objects 1 dirty_or_tx 0] 0x7f9a2c009530)
2024-05-28T16:17:11.855+0530 7f9a5d24c9c0  2 client.4311 cache still has 0+1 items, waiting (for caps to release?)

This commit changes the way Client::_write accepts data. So, now instead of accepting ptr,
iovec array and iovcnt, the helper now accepts a bufferlist which should be contructed by
the caller itself. The reason behind this change is simple - to declutter the API.
For more context checkout this conversation https://github.com/ceph/ceph/pull/58564#discussion_r2000226752

Fixes: https://tracker.ceph.com/issues/66245
Signed-off-by: Dhairya Parmar <dparmar@redhat.com>