handle missing <net/if_dl.h> on Linux, reported by xiaolei zhang <win_hate@163.com>
handle missing <net/if_dl.h> on Linux, reported by xiaolei zhang <win_hate@163.com>

jncornett/libdnet,kbandla/libdnet,kbandla/libdnet,jncornett/libdnet,wtfbbqhax/libdnet,kbandla/libdnet,wtfbbqhax/libdnet,jncornett/libdnet,wtfbbqhax/libdnet