Skip SCTP event initialization if the protocol is not supported

We may not want to actually use SCTP after all, and if we do, we won't
get to use the uninitialized subscribe struct anyway.  Thus aborting
handle initialization is premature here.

libknet/transport_sctp.c

@@ -1322,6 +1322,10 @@ static int _sctp_subscribe_init(knet_handle_t knet_h)
 
 	test_socket = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
 	if (test_socket < 0) {
+		if (errno == EPROTONOSUPPORT) {
+			log_debug(knet_h, KNET_SUB_TRANSP_SCTP, "SCTP not supported, skipping initialization");
+			return 0;
+		}
 		savederrno = errno;
 		log_err(knet_h, KNET_SUB_TRANSP_SCTP, "Unable to create test socket: %s",
 			strerror(savederrno));