[NET]: dev_mcast: unexport dev_mc_upload

dev_mc_add/dev_mc_delete take care of uploading the list when
necessary and thats the only interface other code should use.
Also remove two incorrect calls in DECnet.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>