[PATCH iproute2] Allow to configure /var/run/netns directory

[Pavel Maltsev <pavelm@google.com>]

Currently NETNS_RUN_DIR is hardcoded and refers to /var/run/netns.
However, some systems (e.g. Android) doesn't have /var
which results in error attempts to create network namespaces on these
systems.  This change makes NETNS_RUN_DIR configurable at build time
by allowing to pass environment variable to configre script.

For example: NETNS_RUN_DIR=/mnt/vendor/netns ./configure && make

Tested: verified that iproute2 with configuration mentioned above
creates namespaces in /mnt/vendor/netns

Signed-off-by: Pavel Maltsev <pavelm@google.com>
---
 configure           | 3 +++
 include/namespace.h | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/configure b/configure
index 5ef5cd4c..a6a222da 100755
--- a/configure
+++ b/configure
@@ -213,6 +213,9 @@ EOF
 	echo "IP_CONFIG_SETNS:=y" >>$CONFIG
 	echo "yes"
 	echo "CFLAGS += -DHAVE_SETNS" >>$CONFIG
+	if [ -n "$NETNS_RUN_DIR" ]; then
+		echo "CFLAGS += -DNETNS_RUN_DIR=\\\"$NETNS_RUN_DIR\\\"" >>$CONFIG
+	fi
     else
 	echo "no"
     fi
diff --git a/include/namespace.h b/include/namespace.h
index aed7ce08..b8fb14df 100644
--- a/include/namespace.h
+++ b/include/namespace.h
@@ -8,7 +8,10 @@
 #include <sys/syscall.h>
 #include <errno.h>
 
+#ifndef NETNS_RUN_DIR
 #define NETNS_RUN_DIR "/var/run/netns"
+#endif /* NETNS_RUN_DIR */
+
 #define NETNS_ETC_DIR "/etc/netns"
 
 #ifndef CLONE_NEWNET
-- 
2.17.0.441.gb46fe60e1d-goog