Include <linux/if_ether.h> and <linux/if_infiniband.h> from
nm-utils.h, to get ETH_ALEN and INFINIBAND_ALEN, and remove those
includes (as well as <net/ethernet.h> and <netinet/ether.h>, and
various headers that had been included to get the ARPHRD_* constants)
from other files where they're not needed now.