agents: fix lnx_bonding when no bonding interface is configured

[osedlbauer]

General information

When /proc/net/bonding exists but no bonding interface is configured, head fails with:

head: *: No such file or directory

Fix this by checking if any interfaces exist before running head

Bug reports

• Any Linux system with kmod-bonding loaded but no bonding interface configured (Tested on newest OpenWrt master)
• Reproduce: load bonding kernel module without configuring a bonding interface
• head fails with: head: *: No such file or directory

Proposed changes

• Observed: head fails when /proc/net/bonding exists but is empty
• Expected: empty lnx_bonding section without errors
• Fix: check if interfaces exist before running head

[github-actions]

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[osedlbauer]

I have read the CLA Document and I hereby sign the CLA or my organization already has a signed CLA.

[mo-ki]

Hi! just to clarify: This is just to avoid the line written to stderr, right? Or is there any other impact of the failing head?
If so, I would suggest to just add 2>/dev/null; that would be more explicit about the intention IMHO.