lmsSDR: remove static from struct SamplesPacket.

Th struct SamplesPacket is a type declaration. It is not defined
in memory and thus samplesCount can't be declared static.
Transform it to true cpp static variable class as this is c++ source.

targets/ARCH/LMSSDR/USERSPACE/LIB/lmsSDR/dataTypes.h

@@ -14,14 +14,15 @@ typedef struct
     int16_t q;
 } complex16_t;
 
-typedef struct
+class SamplesPacket
 {
+  public:
     uint64_t timestamp; //timestamp of the packet
     uint16_t first; //index of first unused sample in samples[]
     uint16_t last; //end index of samples
     static const uint16_t samplesCount = 1024; //maximum number of samples in packet
     complex16_t samples[samplesCount]; //must be power of two    
-} SamplesPacket;
+};
 
 complex16_t operator &=(complex16_t & other1, const complex16_t & other) // copy assignment
 {