Change CONFIG_NET_RECEIVE_WONDOW to CONFIG_NET_ETH_TCP_RECVWNDO or CONFIG_NET_SLIP_TCP_RECVWNDO in all defconfig files

Netwoek:  Ada a parameter to netdev_register() to indicate the link protocol supported by the driver.  Use this value to replace some logic commited yesterday

ARP:  Add support for the case where there are multiple networks:  One being Etherenet and the other not (say slip or perhaps someday PPP).  In that case, we need to suppress ARP-related operations on the SLIP/PPP interface only