In prime_cmd.c: add write_vtl_pkt() for symmetry with read_vtl_pkt(); fix the size passed to prime_vtl_pkt() at multiple places; remove outdated, commented code.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Extract function for computing the size of a Prime virtual packet, export it from the library.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Make the "data" argument of cable receive functions a double pointer; use that to optimize several functions in prime_cmd.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Add prime_vtl_pkt_new_with_data_ptr() and hpfiles_ve_create_with_data_ptr() helper functions.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Add support for "send keys" (multiple keys) operation.

Suggested again by Egan Ford.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Rework and improve logging in test_hpcalcs.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>