[Fix firewall work abnormal issue]

[Description]
Fix firewall work abnormal issue
1. add lack kernel config in iptables.cfg
2. reorder kernel config merge order
origin: defconfig->rdkb_cfg->mt7986.cfg
now: defconfig -> mt7986.cfg -> rdkb_cfg

[Release-log]

2 files changed
tree: d101660c5e47d1ca01c3db4dc74d551ecbed2474
  1. classes/
  2. conf/
  3. recipes-connectivity/
  4. recipes-devtools/
  5. recipes-kernel/