add -Wextra to spot more errors in compilation
add -Wextra to spot more errors in compilation

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

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