selftests/net: correct the return value for run_afpackettests

selftests/net: correct the return value for run_afpackettests

BugLink: https://bugs.launchpad.net/bugs/1825778
The run_afpackettests will be marked as passed regardless the return
value of those sub-tests in the script:
    --------------------
    running psock_tpacket test
    --------------------
    [FAIL]
    selftests: run_afpackettests [PASS]

Fix this by changing the return value for each tests.

Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(backported from commit 8c03557c3f25271e62e39154af66ebdd1b59c9ca)
[PHLin: backported with the same logic]
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>