Introduce netdev API

This module provides several operations on network devices
(interfaces), like monitoring changes, setting addresses, routes, link
state, etc.
It also supports managing network interfaces on several different netns
concurrently.

These functionalitites will be used by the tun module included in a
follow-up patch.

Change-Id: I7a00c0445a89e088676a4897061b65196d9197f1
diff --git a/src/core/Makefile.am b/src/core/Makefile.am
index 216330a..04201a8 100644
--- a/src/core/Makefile.am
+++ b/src/core/Makefile.am
@@ -48,6 +48,7 @@
 	loggingrb.c \
 	macaddr.c \
 	msgb.c \
+	netdev.c \
 	netns.c \
 	panic.c \
 	prbs.c \