header: add MNL_ARRAY_SIZE(x)
header: add MNL_ARRAY_SIZE(x)

This patch adds MNL_ARRAY_SIZE(x) which likely to defined over
and over again if you use mnl_cb_run2(...).

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

threatstack/libmnl,cyclops8456/libmnl,remfalc/vyt-libmnl,vyatta/libmnl,Distrotech/libmnl,threatstack/libmnl,greearb/libmnl-ct,Distrotech/libmnl,fqrouter/libmnl,remfalc/vyt-libmnl,chamaken/libmnl,cyclops8456/libmnl,greearb/libmnl-ct,vyos/libmnl,chamaken/libmnl,vyatta/libmnl,cyclops8456/libmnl,vyos/libmnl,fqrouter/libmnl,vyos/libmnl