9p: rename uid and gid parameters

Change the names of 'uid' and 'gid' parameters to the more appropriate
'dfltuid' and 'dfltgid'.  This also sets the default uid/gid to -2
(aka nfsnobody)

Signed-off-by: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

diff --git a/Documentation/filesystems/9p.txt b/Documentation/filesystems/9p.txt
index 1a5f50d..e694cd1 100644
--- a/Documentation/filesystems/9p.txt
+++ b/Documentation/filesystems/9p.txt
@@ -78,9 +78,9 @@
 
   noextend	force legacy mode (no 9p2000.u semantics)
 
-  uid		attempt to mount as a particular uid
+  dfltuid	attempt to mount as a particular uid
 
-  gid		attempt to mount with a particular gid
+  dfltgid	attempt to mount with a particular gid
 
   afid		security channel - used by Plan 9 authentication protocols