ipvs: fix integer overflow in ftp helper port/address parsing

In the Linux kernel, the following vulnerability has been resolved: ipvs: fix integer overflow in ftp helper port/address parsing ip_vs_ftp_get_addrport() accumulates decimal digits into a __u16 (hport) and into unsigned char (p[]) without checking for overflow. A crafted FTP PASV/EPSV response with an over-long port or address octet wraps the value, so the helper configures the data connection with a truncated port/address. The netfilter conntrack FTP helper had the same defect, fixed in commit 2b413fc689ba ("netfilter: nf_conntrack_ftp: avoid u16 overflows"). Apply the equivalent fix here: widen the port accumulator to u32 and reject values above 65535, and reject address octets above 255.