Fetch ethernet receive interrupt entropy futex at every reseed.

This makes us win 8 Bytes per entropy source.  The runtime cost
shouldn't matter because we only rarely call reseed.

Signed-off-by: Hugo Lefeuvre <hugo.lefeuvre@scisemi.com>

sdk/include/platform/arty-a7/platform-entropy.hh

diff --git a/sdk/include/platform/arty-a7/platform-entropy.hh b/sdk/include/platform/arty-a7/platform-entropy.hh
index 341cd8a..6ae2ff1 100644
--- a/sdk/include/platform/arty-a7/platform-entropy.hh
+++ b/sdk/include/platform/arty-a7/platform-entropy.hh
@@ -20,7 +20,6 @@
 class EntropySource
 {
 	ds::xoroshiro::P128R64 prng;
-	const uint32_t        *ethernetInterruptCount;
 
 	public:
 	using ValueType = uint64_t;
@@ -31,8 +30,6 @@
 	/// Constructor, tries to generate an independent sequence of random numbers
 	EntropySource()
 	{
-		ethernetInterruptCount =
-		  interrupt_futex_get(STATIC_SEALED_VALUE(RevokerInterruptEntropy));
 		reseed();
 	}
 
@@ -42,7 +39,8 @@
 		// Start from a not very random seed
 		uint64_t seed = rdcycle64();
 		prng.set_state(seed, seed >> 24);
-		uint32_t interrupts = *ethernetInterruptCount;
+		uint32_t interrupts =
+		  *interrupt_futex_get(STATIC_SEALED_VALUE(RevokerInterruptEntropy));
 		// Permute it with another not-very-random number
 		for (uint32_t i = 0; i < ((interrupts & 0xff00) >> 8); i++)
 		{