Fix sendmsg() implementation

[adamscott]

One-char fix!
Finally, a little more complicated.

This PR introduces a new test. This test calls getifaddrs(), which internally would ultimately call setmsg().

The problem was there: calling getifaddrs() makes dest here undefined, but sock.type === {{{ cDefs.SOCK_DGRAM }}} would be true.

        if (!dest || dest.socket.readyState !== dest.socket.OPEN) {
          // if we're not connected, open a new connection
          if (sock.type === {{{ cDefs.SOCK_DGRAM }}}) {
            if (!dest || dest.socket.readyState === dest.socket.CLOSING || dest.socket.readyState === dest.socket.CLOSED) {
              dest = SOCKFS.websocket_sock_ops.createPeer(sock, addr, port);
            }

The current behaviour would skip then the assignement and dest would be called just after, but throw as dest would be undefined.

My solution is to make sure to set dest even if the sock.type matches. Just to be sure, after the condition, I force the sock type. Therefore, I think the intent of #22630 is respected.

        if (!dest || dest.socket.readyState !== dest.socket.OPEN) {
          // if we're not connected, open a new connection
          if (!dest || sock.type === {{{ cDefs.SOCK_DGRAM }}}) {
            sock.type === {{{ cDefs.SOCK_DGRAM }}};
            if (!dest || dest.socket.readyState === dest.socket.CLOSING || dest.socket.readyState === dest.socket.CLOSED) {
              dest = SOCKFS.websocket_sock_ops.createPeer(sock, addr, port);
            }

Fixes #23046.

[adamscott]

@sbc100 I completely rewrote my PR from the ground up. I added a test, changed the fix, and I updated the PR description.

[adamscott]

@sbc100 ci/circleci seems to break because emcc: error: LLVM version for clang executable "/root/emsdk/upstream/bin/clang" appears incorrect (seeing "21.0", expected "20") [-Wversion-check] [-Werror]