Hi all

Now that RCU applied on 'struct file' seems stable, we can place f_rcuhead in 
a memory location that is not anymore used at call_rcu(&f->f_rcuhead, 
file_free_rcu) time, to reduce the size of this critical kernel object.

The trick I used is to move f_rcuhead and f_list in an union and defining 
macros to access f_list and f_rcuhead

Unfortunatly f_list was also used in IPVS so I had to change 
include/net/ip_vs.h and net/ipv4/ipvs/ip_vs_ctl.c, changing their f_list to 
ipvs_f_list to avoid name clash.

(This is why I send this mail to IPVS maintainers)

Thank you

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>