build: Use $(MAKE) instead of direct call to make

No functional changes, just make it to respect original make binary
name used to start building

Type: improvement

Change-Id: Ic8568237fbb39c6a0d3b7405a9670e9410aeb752
Signed-off-by: Renato Botelho do Couto <renato@netgate.com>
diff --git a/extras/strongswan/vpp_sswan/Makefile b/extras/strongswan/vpp_sswan/Makefile
index 254b90b..85fb506 100644
--- a/extras/strongswan/vpp_sswan/Makefile
+++ b/extras/strongswan/vpp_sswan/Makefile
@@ -76,8 +76,8 @@
 	  echo "SSWAN not downloaded, please run "make" or "make pull-swan" first." ; \
 	  exit 1 ; \
 	fi
-	cd ${SWANDIR} && make -j$(nproc)
-	cd ${SWANDIR} && sudo make install
+	cd ${SWANDIR} && $(MAKE) -j$(nproc)
+	cd ${SWANDIR} && sudo $(MAKE) install
 
 # check if VPP is installed
 ifneq ($(shell test "$(shell ldconfig -p | grep vppinfra.so | awk 'NR==1{print $$1;}')" && echo "yes"), yes)