net: refactor if_clone.c #1

[melifaro]

Summary

• Add ifc_find_cloner()
• Rename current ifc_find_cloner() to ifc_find_cloner_vnet()
• Add ifc_find_cloner_match()

This change simplifies the code a bit and reduces the diff to
the netlink interface cloners merge (D39032).

[melifaro]

.

[kp]

Two non-blocking remarks.

sys/net/if_clone.c

199

That declaration probably needs to be before int error; in line 196, and separated from the assignment.

296

Would ifc_find_cloner_in_vnet() be better?

[glebius]

sys/net/if_clone.c

199

+1 on that