Reinstate checks to handle BU with H bit set

Check for the H flag was omitted in 2276ddec36a3789826842ac8316553fa0702ea89.
This caused TAHI correcpondend node tests 118-123 (5.3. Receiving BU with
(H)bit is set) to fail.

diff --git a/src/cn.c b/src/cn.c
index 0318e9e..a036d96 100644
--- a/src/cn.c
+++ b/src/cn.c
@@ -173,6 +173,10 @@ static int cn_bu_check(struct ip6_mh_binding_update *bu, ssize_t len,
 	int ret;
 
 	non_ind = mh_opt(&bu->ip6mhbu_hdr, mh_opts, IP6_MHOPT_NONCEID);
+
+	if (bu->ip6mhbu_flags & IP6_MH_BU_HOME)
+		return non_ind ? -1 : 0;
+
 	if (!non_ind)
 		return -1;