Always use HTTP handshaking in overlay:

Inbound and outbound peer connections always use HTTP handshakes to
negotiate connections, instead of the deprecated TMHello protocol
message.

rippled versions 0.27.0 and later support both optional HTTP handshakes
and legacy TMHello messages, so always using HTTP handshakes should not
cause disruption. However, versions before 0.27.0 will no longer be
able to participate in the overlay network - support for handshaking
via the TMHello message is removed.

src/ripple/overlay/impl/TMHello.cpp

@@ -27,6 +27,7 @@
 #include <beast/crypto/base64.h>
 #include <beast/http/rfc2616.h>
 #include <beast/module/core/text/LexicalCast.h>
+#include <beast/utility/static_initializer.h>
 #include <boost/regex.hpp>
 #include <algorithm>
 
@@ -170,7 +171,7 @@ appendHello (beast::http::message& m,
 std::vector<ProtocolVersion>
 parse_ProtocolVersions (std::string const& s)
 {
-    static boost::regex const re (
+    static beast::static_initializer<boost::regex> re (
         "^"                  // start of line
         "RTXP/"              // the string "RTXP/"
         "([1-9][0-9]*)"      // a number (non-zero and with no leading zeroes)
@@ -184,7 +185,7 @@ parse_ProtocolVersions (std::string const& s)
     for (auto const& s : list)
     {
         boost::smatch m;
-        if (! boost::regex_match (s, m, re))
+        if (! boost::regex_match (s, m, *re))
             continue;
         int major;
         int minor;