vhost: change vsession->id to uint64_t

This id is assigned from a global increment-only counter
whose type is uint64_t. I believe the original intent
was to use uint64_t for vsession->id as well, let's fix
it now to avoid wrapping errors.

Change-Id: I9cae87e6c74400590a1dc1b1f91d51e4a4c13499
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Vitaliy Mysak <vitaliy.mysak@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/466038


Reviewed-by: Vitaliy Mysak <vitaliy.mysak@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>