ptrace: print request using printxval64

ptrace: print request using printxval64

As first argument of ptrace syscall has a long integer type, print
it using printxval64 because printxval takes unsigned int argument.

* process.c (SYS_FUNC(ptrace)): Change type of "request" variable
from "long" to "unsigned long", print it using printxval64 instead
of printxval.