FHI72: make polling configurable in xran_fh_rx_read_slot(), default off

xran_fh_rx_read_slot() uses polling (a loop over cnt++) to wait for the
next frame/slot. The reasons I have been told is "it does not work
differently", or "there are real-time problems". None of those seem to
be true; by default disable polling, and use the queue instead.

It is possible to enable polling with the cmake option
OAI_FHI72_USE_POLLING=ON. Documentation has been updated to inform about
this change.

radio/fhi_72/CMakeLists.txt

@@ -39,6 +39,8 @@ target_link_libraries(oran_fhlib_5g PRIVATE ${T_LIB})
 # TODO: can be removed?
 target_include_directories(oran_fhlib_5g PRIVATE ${xran_INCLUDE_DIRS}/../src/)
 
+add_boolean_option(OAI_FHI72_USE_POLLING OFF "Enable polling in FHI72 driver" ON)
+
 set_target_properties(oran_fhlib_5g PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
 add_custom_command(TARGET oran_fhlib_5g POST_BUILD
                    COMMAND ${CMAKE_COMMAND} -E create_symlink liboran_fhlib_5g.so liboai_transpro.so

radio/fhi_72/oaioran.c

@@ -39,7 +39,10 @@
 
 #include "common/utils/threadPool/notified_fifo.h"
 
-#define USE_POLLING 1
+#if OAI_FHI72_USE_POLLING
+#define USE_POLLING
+#endif
+
 // Declare variable useful for the send buffer function
 volatile uint8_t first_call_set = 0;
 volatile uint8_t first_rx_set = 0;