configure: update libnetfilter_conntrack version dependency

nfct_labels_get_path() requires libnetfilter_conntrack-1.0.6, update
this dependency.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/configure.ac b/configure.ac
index 74bfcd8..bb9e779 100644
--- a/configure.ac
+++ b/configure.ac
@@ -169,7 +169,7 @@
 
 if test "x$enable_connlabel" = "xyes"; then
 	PKG_CHECK_MODULES([libnetfilter_conntrack],
-		[libnetfilter_conntrack >= 1.0.4],
+		[libnetfilter_conntrack >= 1.0.6],
 		[nfconntrack=1], [nfconntrack=0])
 
 	if test "$nfconntrack" -ne 1; then