compat: define some net constants

To be able to build for 3.0.
net/netlink: add missing compat.h include

On 3.0, we get:
net/netlink.c:32: error: 'NETLINK_CRYPTO' undeclared (first use in this function)
fix broken includes

In 3.0, we get errors like:
/usr/include/linux/netlink.h:34: error: expected specifier-qualifier-list before 'sa_family_t'