net: qrtr: make checks in qrtr_endpoint_post() stricter

These checks are still not strict enough.  The main problem is that if
"cb->type == QRTR_TYPE_NEW_SERVER" is true then "len - hdrlen" is
guaranteed to be 4 but we need to be at least 16 bytes.  In fact, we
can reject everything smaller than sizeof(*pkt) which is 20 bytes.

Also I don't like the ALIGN(size, 4).  It's better to just insist that
data is needs to be aligned at the start.

Fixes: 0baa99ee

 ("net: qrtr: Allow non-immediate node routing")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>