The NLMSG_PUT() macro contains a hidden goto which makes the code hard
to audit and very error prone.

While been there also use the inline function nlmsg_data() instead of the
NLMSG_DATA() macro to do explicit type checking.
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>