selftests/net: report etf errors correctly

The ETF qdisc can queue skbs that it could not pace on the errqueue.

Address a few issues in the selftest

- recv buffer size was too small, and incorrectly calculated
- compared errno to ee_code instead of ee_errno
- missed invalid request error type

v2:
  - fix a few checkpatch --strict indentation warnings

Fixes: ea6a5476

 ("selftests/net: make so_txtime more robust to timer variance")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>