move ARG_ADDRESS handling to separate function
move ARG_RANGE handling out to own function
move ARG_OP handling out to own function
move ARG_LIST handling out to own function
move ARG_RANDOM_PAGE out to own function
move ARG_IOVEC handling out to own function
move ARG_IOVECLEN/SOCKADDRLEN out to own function
move ARG_SOCKADDR handling out to own function
move ARG_MODE_T handling out to own function