selftests: net: py: give bpftrace more time to start

selftests: net: py: give bpftrace more time to start

After commit under Fixes debug runners in the CI hit the following:

  # subprocess.TimeoutExpired: Command '['bpftrace', '-f', 'json', '-q', '-e', 'kprobe:netpoll_poll_dev { @hits = count(); } interval:s:10 { exit(); }']' timed out after 15 seconds
  # # Exception| net.lib.py.ksft.KsftFailEx: bpftrace failed to run!?: {}

in netpoll_basic.py >10% of the time. Let's give bpftool more time
to start, it can take a while on a debug kernel.

Fixes: 82562972b854 ("selftests: net: pass bpftrace timeout to cmd()")
Reviewed-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Link: https://patch.msgid.link/20260315160038.3187730-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>