Segfaults with musl

[sbyx]

musl has screwed up definition of msghdr (used 4x in mrib.c).
Positional initialization breaks and needs to be converted:

struct msghdr hdr = {&from, sizeof(from), &iov, 1, cbuf, sizeof(cbuf), 0};

to

struct msghdr hdr = {
.msg_name = &from,
.msg_namelen = sizeof(from),
...
}