man: Fix default value of AuthDirGuardBWGuarantee to 2MB

Closes #20435

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/bug20435

@@ -0,0 +1,4 @@
+  o Documentation (man page):
+    - Set the default value from 250 KBytes to 2 MBytes for
+      AuthDirGuardBWGuarantee in the man page which is what the code is using;
+      bugfix on tor-0.2.5.6-alpha; Closes ticket 20345.

doc/tor.1.txt

@@ -2248,7 +2248,7 @@ on the public Tor network.
 [[AuthDirGuardBWGuarantee]] **AuthDirGuardBWGuarantee** __N__ **bytes**|**KBytes**|**MBytes**|**GBytes**|**KBits**|**MBits**|**GBits**::
     Authoritative directories only. If non-zero, this advertised capacity
     or more is always sufficient to satisfy the bandwidth requirement
-    for the Guard flag. (Default: 250 KBytes)
+    for the Guard flag. (Default: 2 MBytes)
 
 [[AuthDirPinKeys]] **AuthDirPinKeys** **0**|**1**::
     Authoritative directories only. If non-zero, do not allow any relay to