uhd: Fix radio_control-related method constness

The const-ness of some radio_control differed between base class and
implementation. This fixes the consistency, but also makes sure these
methods follow the rules for when to make methods 'const'.

The following rules apply:
- Methods that query static capabilities are const. Here, we made
  get_tx_lo_sources() const (the RX version was already const).
- Getters that may have to interact with the device (e.g., peek
  a register) are not const, because the act of peeking is usually also
  non-const. Here, we changed get_rx_lo_export_enabled() to non-const.
- All base classes are fixed such that the derived classes and the base
  classes have the same const-ness. Clang was warning about differences.
  This can cause very tricky bugs, where the radio_control_impl version
  can get called instead of the intended child class.

1 files changed, 2 insertions, 3 deletions

diff --git a/host/include/uhd/rfnoc/rf_control/core_iface.hpp b/host/include/uhd/rfnoc/rf_control/core_iface.hpp
index 9b780b3c8..ff7ec3550 100644
--- a/host/include/uhd/rfnoc/rf_control/core_iface.hpp
+++ b/host/include/uhd/rfnoc/rf_control/core_iface.hpp
@@ -326,8 +326,7 @@ public:
      * \param name the name of the LO stage to query
      * \param chan the channel index 0 to N-1
      */
-    virtual bool get_rx_lo_export_enabled(
-        const std::string& name, const size_t chan) const = 0;
+    virtual bool get_rx_lo_export_enabled(const std::string& name, const size_t chan) = 0;
 
     /*!
      * Set the RX LO frequency (Advanced).
@@ -365,7 +364,7 @@ public:
      * \return a vector of strings for possible settings
      */
     virtual std::vector<std::string> get_tx_lo_sources(
-        const std::string& name, const size_t chan) = 0;
+        const std::string& name, const size_t chan) const = 0;
 
     /*!
      * Get the LO frequency range of the tx LO.