zerotier-one: Fix libnatpmp build

The zerotier-one build required libnatpmp, but it based this on /usr/lib
rather than the local cross-compilation environment.

The make-linux.mk Makefile is fairly unconventional with limited
configuration macros.  But a particular combination of macro and
environment variable configuration allows us to both build the local
exp/libnatbib source, and to integrate it into the zerotier-one build.

projects/ROCKNIX/packages/network/zerotier-one/package.mk

@@ -19,7 +19,13 @@ pre_unpack() {
 
 
 make_target() {
+    # Build libnatpmp for target
+    make -C ${PKG_BUILD}/ext/libnatpmp CC=${CC}
+
+	# Build zerotier-one
     cd ${PKG_BUILD}
+    CPPFLAGS="${CPPFLAGS} -I${PKG_BUILD}/ext/libnatpmp" \
+    LDLIBS="${LDLIBS} -L${PKG_BUILD}/ext/libnatpmp" \
     make -f make-linux.mk ZT_SSO_SUPPORTED=0 one
 }