linux: allow RTM_GETADDR without full ifaddrmsg argument

Even modern glibc uses truncated argument for RTM_GETADDR when it wants to
list all addresses in a system. See
sysdeps/unix/sysv/linux/ifaddrs.c:netlink_sendreq(). It sends a one
char payload. Linux kernel allows that as long as given socket is not
marked as a 'strict'. We have a similar flag in the general netlink code
and it is checked in
sys/netlink/netlink_message_parser.h:nl_parse_header(). If the flag is
not present, parser will allocate a temporary zeroed buffer to make the
message correct. The checks added in b977dd1ea5fb blocked such message
before the parser. My reading of glibc says that there are two types of
messages that are sent with netlink_sendreq() - RTM_GETLINK and
RTM_GETADDR. The RTM_GETLINK is binary compatible between Linux and
FreeBSD and thus doesn't need any ABI handler.

PR: 279012
Fixes: b977dd1ea5fbc2df3f1279330be4d089322eb2cf