This patch removes filp_count_lock spinlock, used to protect files_stat.nr_files.

Just use atomic_t type and atomic_inc()/atomic_dec() operations.

This patch assumes that atomic_read() is a plain {return v->counter;} on all 
architectures. (keywords : sysctl, /proc/sys/fs/file-nr, proc_dointvec)

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