libnl: include limits.h to fix build failure

Fixes the ULONG_MAX definition problem:

In file included from cache.c:43:
../include/netlink-local.h: In function '__str2type':../include/netlink-local.h:218: error: 'ULONG_MAX' undeclared (first use in this function)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>