nftables: disable dblatex check

On the systems with old dblatex (for example 3.0) the build step will
fail, because dblatex doesn't support '-q' parameter. This patch
overrides dblatex check.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/nftables/nftables.mk

@@ -12,4 +12,6 @@ NFTABLES_DEPENDENCIES = gmp libmnl libnftnl readline host-bison host-flex \
 NFTABLES_LICENSE = GPLv2
 NFTABLES_LICENSE_FILES = COPYING
 
+NFTABLES_CONF_ENV = ac_cv_prog_CONFIG_PDF=no
+
 $(eval $(autotools-package))