Introduce netns API

Write a new API and implementation to manage network namespace related
operations.

This will be used by the upcoming tundev module.

Change-Id: I0f2fba2fa42250a07211a7b7f479498f27c529da
diff --git a/src/core/Makefile.am b/src/core/Makefile.am
index 9b812ce..216330a 100644
--- a/src/core/Makefile.am
+++ b/src/core/Makefile.am
@@ -48,6 +48,7 @@
 	loggingrb.c \
 	macaddr.c \
 	msgb.c \
+	netns.c \
 	panic.c \
 	prbs.c \
 	prim.c \