arp: stop using globals

function                                             old     new   delta
hw_set                                                 1       -      -1
arp_main                                            1559    1558      -1
sockfd                                                 8       4      -4
hw                                                     4       -      -4
device                                                 4       -      -4
ap                                                     4       -      -4
packed_usage                                       25402   25393      -9
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(add/remove: 0/4 grow/shrink: 0/3 up/down: 0/-27)             Total: -27 bytes

2 files changed