migration: qemu_file_set_blocking(): add errp parameter

migration: qemu_file_set_blocking(): add errp parameter

qemu_file_set_blocking() is a wrapper on qio_channel_set_blocking(),
so let's passthrough the errp.

Note the migration should not be using &error_abort in these calls,
however, this is done to expedite the API conversion.

The original code would have eventually ended up calling either
qemu_socket_set_nonblock which would asset on Linux, or
g_unix_set_fd_nonblocking which would propagate errors. We never
saw asserts in practice, and conceptually they should not happen,
but ideally this code will be later adapted to remove use of
&error_abort.

Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>