capabilities: add bounding set to /proc/self/status

There is currently no way to query the bounding set of another task. As there
appears to be no security reason not to, and as Michael Kerrisk points out the
following valid reasons to do so exist:

* consistency (I can see all of the other per-thread/process sets in
/proc/.../status)

* debugging -- I could imagine that it would make the job of debugging an
application that uses capabilities a little simpler.

this patch adds the bounding set to /proc/self/status right after the
effective set.

Signed-off-by: Serge E. Hallyn <[e-mail]>
Acked-by: Michael Kerrisk <[e-mail]>
Acked-by: Andrew G. Morgan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/proc/array.c

···
 	render_cap_t(m, "CapInh:\t", &p->cap_inheritable);
 	render_cap_t(m, "CapPrm:\t", &p->cap_permitted);
 	render_cap_t(m, "CapEff:\t", &p->cap_effective);
+	render_cap_t(m, "CapBnd:\t", &p->cap_bset);
 }
 
 static inline void task_context_switch_counts(struct seq_file *m,