ppp: remove gethostby*() calls

[yanhaowang]

Summary

1. Use getaddrinfo to replace gethostbyname, use for loop to loop the address list and copy the first meet ipv4 address.

[yanhaowang]

• Remove unused variable

[yanhaowang]

• Remove for loop

[yanhaowang]

Update according Hiroki advise in D45594

1. Use "error" instead of "status" name to store the value of getaddrinfo() function.
2. Use compound literals instead of "hints" variable.

[yanhaowang]

Remove unused variable

[yanhaowang]

Fix format