header: use sysconf() instead of getpagesize()
header: use sysconf() instead of getpagesize()

The sysconf(_SC_PAGESIZE) call is more portable since it does not need
_BSD_SOURCE defined.

Signed-off-by: Pablo Neira Ayuso <707d14912bb250caf67dfe0ea4035681fbfc4f56@netfilter.org>

greearb/libmnl-ct,greearb/libmnl-ct,chamaken/libmnl,chamaken/libmnl