loader: don't disable rp-filter for IPsec

[julianwiedmann]

This was added all the way back with 79b4eba ("cilium: encrypt-node needs rp_filter zerod otherwise packets are lost"), which matches the error message in that it's about encryption for node IPs.

But as IPsec now only supports pod-to-pod traffic, we can likely remove this part.

[julianwiedmann]

/test

[julianwiedmann]

Credit to @ysksuzuki for digging up all the code locations where we currently manage the RP filter!

We've had slight concerns that the two cases below might even conflict - so it's great if we can clean this up:

• Disable rp_filter on network facing interface to encrypt over if IPSec is Enabled
  

  cilium/pkg/datapath/loader/base.go

  Line 210 in 6b8c995

  if err := connector.DisableRpFilter(l.sysctl, iface); err != nil {

• Disable rp_filter on a device with default route if IPAM mode is IPAMENI
  

  cilium/pkg/datapath/loader/base.go

  Line 128 in 6b8c995

  Name: fmt.Sprintf("net.ipv4.conf.%s.rp_filter", iface.Attrs().Name),