syscall: rename method Flock_t.Lock to func FcntlFlock
syscall: rename method Flock_t.Lock to func FcntlFlock

Update Issue 7059

R=rsc
CC=golang-codereviews
https://codereview.appspot.com/55370043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang