Add RDMA ibverb driver plugin

RDMA ibverb is a userspace API to efficiently rx/tx packets. This is an
initial, unoptimized driver targeting Mellanox cards.
Next steps should include batching, multiqueue and additional cards.

Change-Id: I0309c7a543f75f2f9317eaf63ca502ac7a093ef9
Signed-off-by: Benoît Ganne <bganne@cisco.com>
diff --git a/build/external/packages.mk b/build/external/packages.mk
index 4056b2f..005c2a9 100644
--- a/build/external/packages.mk
+++ b/build/external/packages.mk
@@ -31,12 +31,12 @@
 downloads/$($1_tarball):
 	mkdir -p downloads
 	@if [ -e $(DL_CACHE_DIR)/$($1_tarball) ] ; \
-		then cp $(DL_CACHE_DIR)/$($1_tarball) downloads/ ; \
+		then cp $(DL_CACHE_DIR)/$($1_tarball) $$@ ; \
 	else \
 		echo "Downloading $($1_url)" ; \
-		curl -o downloads/$($1_tarball) -LO $($1_url) ; \
+		curl -o $$@ -LO $($1_url) ; \
 	fi
-	@rm -f $(B)/.download.ok
+	@rm -f $(B)/.$1.download.ok
 
 $(B)/.$1.download.ok: downloads/$($1_tarball)
 	@mkdir -p $(B)