selftest: netcons: refactor target creation

selftest: netcons: refactor target creation

Extract the netconsole target creation from create_dynamic_target(), by
moving it from create_dynamic_target() into a new helper function. This
enables other tests to use the creation of netconsole targets with
arbitrary parameters and no sleep.

The new helper will be utilized by forthcoming torture-type selftests
that require dynamic target management.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251107-netconsole_torture-v10-2-749227b55f63@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>