Merge bitcoin#22200: zmq: use std::string in zmqError()

3f05a9e zmq: use msg: prefix over errno= in zmqError (fanquake)
9a7cb57 zmq: use std::string in zmqError() (fanquake)

Pull request description:

  This is two minor changes. The first is to change `zmqError` to take a `const std::string&` instead of a `const char*`. The second is to change the second portion of `zmqError` to print `msg: message` rather than `errno=message`, given that `zmq_strerror` returns a message. To me, this seems more readable / useful than output like: `Error: Unable to initialize context errno=No such file or directory`.

ACKs for top commit:
  practicalswift:
    cr ACK 3f05a9e
  instagibbs:
    utACK bitcoin@3f05a9e
  theStack:
    Code-Review ACK 3f05a9e

Tree-SHA512: 197cf381e8b3ced271d0e575e0c6d8e5e9ed93c4b284338b17873c5232eaabe64d6c4b66e1aeb5e76befc89e316abae2b28b7fd760f178481d7b9f4e3f85da67

src/zmq/zmqutil.cpp

@@ -5,10 +5,12 @@
 #include <zmq/zmqutil.h>
 
 #include <logging.h>
-
 #include <zmq.h>
 
-void zmqError(const char* str)
+#include <cerrno>
+#include <string>
+
+void zmqError(const std::string& str)
 {
-    LogPrint(BCLog::ZMQ, "zmq: Error: %s, errno=%s\n", str, zmq_strerror(errno));
+    LogPrint(BCLog::ZMQ, "zmq: Error: %s, msg: %s\n", str, zmq_strerror(errno));
 }

src/zmq/zmqutil.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_ZMQ_ZMQUTIL_H
 #define BITCOIN_ZMQ_ZMQUTIL_H
 
-void zmqError(const char* str);
+#include <string>
+
+void zmqError(const std::string& str);
 
 #endif // BITCOIN_ZMQ_ZMQUTIL_H