ss: Add support for retrieving SELinux contexts

The process SELinux contexts can be added to the output using the -Z
option. Using the -z option will show the process and socket contexts (see
the man page for details).
For netlink sockets: if valid process show process context, if pid = 0
show kernel initial context, if unknown show "unavailable".

Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>
diff --git a/configure b/configure
index da01c19..d5170f0 100755
--- a/configure
+++ b/configure
@@ -231,6 +231,18 @@
     rm -f $TMPDIR/ipsettest.c $TMPDIR/ipsettest
 }
 
+check_selinux()
+# SELinux is a compile time option in the ss utility
+{
+	if ${PKG_CONFIG} libselinux --exists
+	then
+		echo "HAVE_SELINUX:=y" >>Config
+		echo "yes"
+	else
+		echo "no"
+	fi
+}
+
 echo "# Generated config based on" $INCLUDE >Config
 check_toolchain
 
@@ -253,3 +265,6 @@
 
 echo -n "libc has setns: "
 check_setns
+
+echo -n "SELinux support: "
+check_selinux