[PATCH] netlink: add signed types

Signed types might be needed in NL communication from time to time
(I need s32 in team driver), so add them.

Change-Id: Icc6c8286a1d55313fcc7993d8b02267fe1ef2bdc
CRs-Fixed: 677858
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>