rtnetlink: do not use RTM_GETLINK directly

Userspace sends RTM_GETLINK type, but the kernel substracts
RTM_BASE from this, i.e. 'type' doesn't contain RTM_GETLINK
anymore but instead RTM_GETLINK - RTM_BASE.

This caused the calcit callback to not be invoked when it
should have been (and vice versa).

While at it, also fix a off-by one when checking family index. vs
handler array size.

Fixes: e1fa6d21

 ("rtnetlink: call rtnl_calcit directly")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>