ncp: Allow underspecification of remove command for IPV6_ADDRESS_TABLE. (#875)

For removal operations, Spinel allows you to underspecify the entry
in question by omitting any fields after the "key" field, since they
would be ignored anyway. Without this change, underspecified IPV6 address
removals will fail.

src/ncp/ncp_base.cpp

@@ -4575,11 +4575,8 @@ ThreadError NcpBase::RemovePropertyHandler_IPV6_ADDRESS_TABLE(uint8_t header, sp
     parsedLength = spinel_datatype_unpack(
                        value_ptr,
                        value_len,
-                       "6CLL",
-                       &addr_ptr,
-                       NULL,
-                       NULL,
-                       NULL
+                       "6",
+                       &addr_ptr
                    );
 
     if (parsedLength > 0)