tests: include sys/socket.h before linux/if_arp.h
tests: include sys/socket.h before linux/if_arp.h

This is how it has to be accoding to the man page.

PiperOrigin-RevId: 281998068

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor