MFC r332151:

ifconf(): correct handling of sockaddrs smaller than struct sockaddr.

Portable programs that use SIOCGIFCONF (e.g. traceroute) assume
that each pseudo ifreq is of length MAX(sizeof(struct ifreq),
sizeof(ifr_name) + ifr_addr.sa_len). For short sockaddrs we copied
too much from the source sockaddr resulting in a heap leak.

I believe only one such sockaddr exists (struct sockaddr_sco which
is 8 bytes) and it is unclear if such sockaddrs end up on interfaces
in practice. If it did, the result would be an 8 byte heap leak on
current architectures.

admbugs: 869
Reviewed by: kib
Obtained from: CheriBSD
Security: kernel heap leak
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D14981