spc: fix corrupted modesense pages

Two argumens were swapped in the header to the function for safe writing to the data-out buffer with
the result that any/all modesense data-in we send back to the initiator are mainly garbage.

Fix this and also add tests for this to libiscsi so that we can catch any future regressions :

    ./bin/iscsi-test-cu iscsi://127.0.0.1/iqn.ronnie.test/1 --test SCSI.ModeSense6.AllPages -V

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
DOCS: Add --bsoflags and sync/direct to the manpage

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>