Fixing MacOS / Clang builds
!1253 (merged) changed the type of client_ip to std::string, which triggered an error when compiled with -Wnon-pod-varargs with clang.
Fixed with by calling c_str().
I'm lacking a mac for testing, but tested the fix with:
qmake QMAKE_CXX=clang++ QMAKE_CC=clang QMAKE_LINK=clang++ QMAKE_CXXFLAGS=-Wno-narrowing