Use "se" instead of "f" for struct fuse_session

Use "se" instead of "f" for struct fuse_session

The fuse_session pointer is sometimes called f and at other times
se. The former is an artifact from the time when there still was a
separate struct fuse_ll object.

For consistency and to easy maintenance, this patch changes the name of
the fuse_session pointer to "se" wherever possible.

This patch was generated by the following Coccinelle script:

@@
symbol f, se;
@@
struct fuse_session *
-f
+se
;
<...
-f
+se
...>

@@
expression expr;
@@
struct fuse_session *
-f
+se
= expr;
<...
-f
+se
...>

@@
identifier fn;
@@
fn(...,struct fuse_session *
-f
+se
,...) { <...
-f
+se
...> }

Due to its complexity, the do_init() function had to be commented out
and then patched manually.