eth: Make is_link_local() consistent with other address tests

Function name should include '_ether_addr'.
Return type should be bool.
Parameter name should be 'addr' not 'dest' (also matching kernel-doc).

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>