agent: move the iptables bridge forwarding disable to agent register

[mingshuoqiu]

The DisableBridgeNF() placed in init() would cause phantom error message while restart/kill the network-manager pod. Move it to agent register to prevent the unexpected invoke.

Fixes: 6521629 ("Disable iptables bridge forwarding on initializatio")

Problem:
harvester/harvester#6747

Solution:
Move the DisableBridgeNF() to agent register to prevent the unexpected invoke.

Related Issue:

Test plan:

1. Manually restarting the harvester-network-controller-manager deployment or simply killing off the pod
2. check if there's the error message disable net.bridge.bridge-nf-call-iptables failed, error: open /proc/sys/net/bridge/bridge-nf-call-iptables: read-only file system

[starbops]

Confirmed that

• Manager pods no longer crash
• Only agent pods set the kernel tunable
• Each node's net.bridge.bridge-nf-call-iptables is 0.

LGTM, thank you.

[starbops]

@mergify backport v0.5.x

[mergify]

backport v0.5.x

✅ Backports have been created

• #124 agent: move the iptables bridge forwarding disable to agent register (backport #123) has been created for branch v0.5.x