MEDIUM: tune.http.maxhdr makes it possible to configure the maximum number of HTTP headers

For a long time, the max number of headers was taken as a part of the buffer
size. Since the header size can be configured at runtime, it does not make
much sense anymore.

Nothing was making it necessary to have a static value, so let's turn this into
a tunable with a default value of 101 which equals what was previously used.
diff --git a/include/common/defaults.h b/include/common/defaults.h
index 0a4f420..8647131 100644
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -58,9 +58,9 @@
 #define	MAX_MATCH       10
 
 // max # of headers in one HTTP request or response
-// By default, about 100 headers per 8 kB.
+// By default, about 100 headers (+1 for the first line)
 #ifndef MAX_HTTP_HDR
-#define MAX_HTTP_HDR    ((BUFSIZE+79)/80)
+#define MAX_HTTP_HDR    101
 #endif
 
 // max # of headers in history when looking for header #-X