isisd, lib: Fix some more compiler warnings

A couple compiler warnings snuck in from the last
round of work being looked at.  This cleans them up

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/isisd/isis_bpf.c b/isisd/isis_bpf.c
index fd65608..889b4c3 100644
--- a/isisd/isis_bpf.c
+++ b/isisd/isis_bpf.c
@@ -348,6 +348,8 @@
         return ISIS_WARNING;
       return ISIS_ERROR;
     }
+
+  return ISIS_OK;
 }
 
 int