s3: smb2 read sendfile

[sebastien.laveze at mindspeed.com]

Hi all,
So first of all I don't know if the source3 build is still maintained in 
master and 4.x branch.
However I needed to use the source3 code in 4.x branch because it does 
include some features (e.g. largeMTU support) which are not present in the 
stable 3.6.x release.

So maybe a first question would be if this is a reasonable choice ? :)

Second point is (which may be irrelevant if the source3 code is not 
maintained anymore)I found that the schedule_smb2_sendfile_read never uses 
the sendfile option in a regular SMB2 test with a windows client.

There's a bunch of checks before deciding to use sendfile especially this 
one meant (if I understand correctly) to prevent using sendfile with 
compound messages:

smb2req->in.vector_count < (2*SMBD_SMB2_NUM_IOV_PER_REQ)

which always fail in my case even if my client never sends compound 
message. 

So guess the correct check would be more like it is in stable branches:

smb2req->in.vector_count != (SMBD_SMB2_NUM_IOV_PER_REQ + 1)

I mostly want to be sure I'm not gonna break something with this fix.


Thanks,
Sebastien