dnsmasq: move feature detection inside a shell func

Resolves openwrt/packages#9219

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

package/network/services/dnsmasq/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=dnsmasq
 PKG_UPSTREAM_VERSION:=2.80
 PKG_VERSION:=$(subst test,~~test,$(subst rc,~rc,$(PKG_UPSTREAM_VERSION)))
-PKG_RELEASE:=12
+PKG_RELEASE:=13
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_UPSTREAM_VERSION).tar.xz
 PKG_SOURCE_URL:=http://thekelleys.org.uk/dnsmasq

package/network/services/dnsmasq/files/dnsmasq.init

@@ -22,15 +22,18 @@ DHCPSCRIPT="/usr/lib/dnsmasq/dhcp-script.sh"
 
 DNSMASQ_DHCP_VER=4
 
-dnsmasq_features="$(dnsmasq --version | grep -m1 'Compile time options:' | cut -d: -f2) "
-[ "${dnsmasq_features#* DHCP }" = "$dnsmasq_features" ] || dnsmasq_has_dhcp=1
-[ "${dnsmasq_features#* DHCPv6 }" = "$dnsmasq_features" ] || dnsmasq_has_dhcp6=1
-[ "${dnsmasq_features#* DNSSEC }" = "$dnsmasq_features" ] || dnsmasq_has_dnssec=1
-[ "${dnsmasq_features#* TFTP }" = "$dnsmasq_features" ] || dnsmasq_has_tftp=1
-[ "${dnsmasq_features#* ipset }" = "$dnsmasq_features" ] || dnsmasq_has_ipset=1
 dnsmasq_ignore_opt() {
 	local opt="$1"
 
+	if [ -z "$dnsmasq_features" ]; then
+		dnsmasq_features="$(dnsmasq --version | grep -m1 'Compile time options:' | cut -d: -f2) "
+		[ "${dnsmasq_features#* DHCP }" = "$dnsmasq_features" ] || dnsmasq_has_dhcp=1
+		[ "${dnsmasq_features#* DHCPv6 }" = "$dnsmasq_features" ] || dnsmasq_has_dhcp6=1
+		[ "${dnsmasq_features#* DNSSEC }" = "$dnsmasq_features" ] || dnsmasq_has_dnssec=1
+		[ "${dnsmasq_features#* TFTP }" = "$dnsmasq_features" ] || dnsmasq_has_tftp=1
+		[ "${dnsmasq_features#* ipset }" = "$dnsmasq_features" ] || dnsmasq_has_ipset=1
+	fi
+
 	case "$opt" in
 		dhcp-duid|\
 		ra-param)