CDP: fix "Unchecked return value" found by Coverity

The bounds check is already done before by ND_TCHECK2(*tptr, len).
So we are deliberately ignoring the return values of fn_printn with last
argument NULL (no bounds check).
OLSR: fix "Unchecked return value" found by Coverity

The bounds check is already done before by ND_TCHECK2(*msg_data, addr_size +
name_entry_len + name_entry_padding).
So we are deliberately ignoring the return values of fn_printn with last
argument NULL (no bounds check).
BOOTP/DHCP: fix "Unchecked return value" found by Coverity

Add a bounds check
Fix spaces