read_repair_decision: fix operator<<(std::ostream&, ...)

Argument-dependent lookup requires that the operator be declared in the
same namespace as the class; move it there.

While at it, de-static it, it only causes bloat.

db/read_repair_decision.hh

@@ -49,9 +49,7 @@ enum class read_repair_decision {
   DC_LOCAL
 };
 
-}
-
-static inline std::ostream&  operator<<(std::ostream& out, db::read_repair_decision d) {
+inline std::ostream&  operator<<(std::ostream& out, db::read_repair_decision d) {
     switch (d) {
     case db::read_repair_decision::NONE: out << "NONE"; break;
     case db::read_repair_decision::GLOBAL: out << "GLOBAL"; break;
@@ -60,3 +58,5 @@ static inline std::ostream&  operator<<(std::ostream& out, db::read_repair_decis
     }
     return out;
 }
+
+}