Bump minrelaytxfee default

To bridge the time until a dynamic method for determining this fee is
merged.

This is especially aimed at the stable releases (0.10, 0.11) because
full mempool limiting, as will be in 0.12, is too invasive and risky to
backport.

Github-Pull: #6793
Rebased-From: 28e3249e53b8ef7516636df0f1406466a513095d 4e2efb3c5fde4b1e332cc032e3dc4082ec4e3cac

src/main.cpp

@@ -64,7 +64,7 @@ uint64_t nPruneTarget = 0;
 bool fAlerts = DEFAULT_ALERTS;
 
 /** Fees smaller than this (in satoshi) are considered zero fee (for relaying and mining) */
-CFeeRate minRelayTxFee = CFeeRate(1000);
+CFeeRate minRelayTxFee = CFeeRate(5000);
 
 CTxMemPool mempool(::minRelayTxFee);