MINOR: ssl: use MAXPATHLEN instead of PATH_MAX

Apollon Oikonomopoulos reported a build failure on Hurd where PATH_MAX
is not defined. The only place where it is referenced is ssl_sock.c,
all other places use MAXPATHLEN instead, with a fallback to 128 when
the OS does not define it. So let's switch to MAXPATHLEN as well.
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index ce1712d..8169d78 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -2543,14 +2543,14 @@
 /* parse the "crt" bind keyword */
 static int bind_parse_crt(char **args, int cur_arg, struct proxy *px, struct bind_conf *conf, char **err)
 {
-	char path[PATH_MAX];
+	char path[MAXPATHLEN];
 	if (!*args[cur_arg + 1]) {
 		memprintf(err, "'%s' : missing certificate location", args[cur_arg]);
 		return ERR_ALERT | ERR_FATAL;
 	}
 
 	if ((*args[cur_arg + 1] != '/' ) && global.crt_base) {
-		if ((strlen(global.crt_base) + 1 + strlen(args[cur_arg + 1]) + 1) > PATH_MAX) {
+		if ((strlen(global.crt_base) + 1 + strlen(args[cur_arg + 1]) + 1) > MAXPATHLEN) {
 			memprintf(err, "'%s' : path too long", args[cur_arg]);
 			return ERR_ALERT | ERR_FATAL;
 		}