bpf: Replace l3_off by its constant value
bpf: Replace l3_off by its constant value

Variable l3_off is actually always a constant so we can just use the
constant directly. That makes it clear to the reader that it won't
change.

Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium