Reduces scope to where it is really used given this creates a map.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

When the agent starts up we can see the following maps being removed as
stale maps:

  [...]
  level=info msg="Restored endpoint" endpointID=3747 ipAddr="[ ]" subsys=endpoint
  level=info msg="Finished regenerating restored endpoints" regenerated=1 subsys=daemon total=1
  level=info msg="Removed stale bpf map" file-path=/sys/fs/bpf/tc/globals/cilium_capture_cache subsys=daemon
  level=info msg="Removed stale bpf map" file-path=/sys/fs/bpf/tc/globals/cilium_ktime_cache subsys=daemon
  [...]

This is due to pcap.h being included from nodeport.h where the former
defines mentioned maps unconditionally. Rework it, so that both are
only created in L4LB mode.

Fixes: #17935
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>