libreswan: add libunbound and minor fixes

enable libunbound, along with dependency

add kmod-crypto-aead kmod-crypto-gcm dependency to support AES GCM

disable libseccomp
  /git/openwrt/build_dir/target-mips_24kc_musl/libreswan-3.27/include/lswseccomp.h:24:10: fatal error: seccomp.h: No such file or directory
  #include <seccomp.h>
          ^~~~~~~~~~~
add missing dependency nspr

add nss-utils dependency to able to import x509 Certificates  to fix the error
 ipsec import west.p12
 /usr/sbin/ipsec: line 239: pk12util: not found
 /usr/sbin/ipsec: line 84: certutil: not found

remove libnss dependency, nss-utils  util will pull it.
remove unused build option KERNELSRC not necesscay since b4b98e2922.

Signed-off-by: Antony Antony <antony@phenome.org>

net/libreswan/Makefile

@@ -39,9 +39,11 @@ $(call Package/libreswan/Default)
   SUBMENU:=VPN
   SECTION:=net
   CATEGORY:=Network
-  DEPENDS:= +libnss +librt +libevent2 +libevent2-pthreads +kmod-crypto-authenc \
-	+kmod-crypto-hash +kmod-ipt-ipsec +iptables-mod-ipsec +ip-full +kmod-ip-vti \
-	+kmod-ipsec +kmod-ipsec4 +kmod-crypto-rng +IPV6:kmod-ipsec6 +IPV6:kmod-ip6-vti
+  DEPENDS:= +IPV6:kmod-ip6-vti +IPV6:kmod-ipsec6 +ip-full +iptables-mod-ipsec \
+	+kmod-crypto-aead +kmod-crypto-authenc +kmod-crypto-gcm \
+	+kmod-crypto-hash +kmod-crypto-rng +kmod-ip-vti +kmod-ipsec \
+	+kmod-ipsec4 +kmod-ipt-ipsec +libevent2 +libevent2-pthreads \
+	+libldns +librt +libunbound-heavy +nss-utils +nspr
   PROVIDES:=openswan
   CONFLICTS:=strongswan
   TITLE+= IPsec Server
@@ -61,10 +63,8 @@ define Package/libreswan/conffiles
 /etc/ipsec.secrets
 endef
 
-TARGET_CFLAGS+= -Wno-error=format-nonliteral
 MAKE_FLAGS+= \
     WERROR_CFLAGS=" " \
-    USE_DNSSEC=false \
     USE_LINUX_AUDIT=false \
     USE_LABELED_IPSEC=false \
     USE_NM=false \
@@ -74,10 +74,10 @@ MAKE_FLAGS+= \
     USE_FIPSCHECK=false \
     USE_LIBCAP_NG=false \
     USE_SYSTEMD_WATCHDOG=false \
+    USE_SECCOMP=false\
     INC_USRLOCAL="/usr" \
     FINALRUNDIR="/var/run/pluto" \
     ARCH="$(LINUX_KARCH)" \
-    KERNELSRC="$(LINUX_DIR)"
 
 define Build/Prepare
 	$(call Build/Prepare/Default)