include/linux/if_ether.h: Add #define ETH_P_LINK_CTL for HPNA and wlan local tunnel

Ethertype used by HPNA control protocols (LARQ, rate, link, etc) and by
Broadcom wlan drivers for local signalling.

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>