Spotted by: Coverity

Spotted by our Alpine Linux job on CircleCI.

Change CLI cmd debug.xid to set the next XID to be used, rather than "one less than the next XID to be used"

Opportunity noticed during the review of #3872.

This is an enhanced fix for #1777

Fixes #3882

Otherwise a long banner may throw expectations off by one line.

Fixes #3877

Neither Martin nor I can remember why this was uintptr_t in the first
place, and there is no signs of pointers anywhere nearby.

Refs #3874

It makes no sense to emit this just before we end the transaction,
except to help varnishncsa find the client IP address.

Upon success we expect a non-null pointer, and to make sure this is not
residual uninitialized stack memory, it is null'd beforehand.

    /bin/varnishd/cache/cache_acceptor.c: 375 in vca_mk_tcp()
    369     {
    370             struct suckaddr *sa;
    371             ssize_t sz;
    372
    373             AN(SES_Reserve_remote_addr(sp, &sa, &sz));
    374             assert(sz == vsa_suckaddr_len);
    >>>     CID 1517259:  Resource leaks  (RESOURCE_LEAK)
    >>>     Failing to save or free storage allocated by "VSA_Build(sa, &wa->acceptaddr, wa->acceptaddrlen)" leaks it.
    375             AN(VSA_Build(sa, &wa->acceptaddr, wa->acceptaddrlen));
    376             sp->sattr[SA_CLIENT_ADDR] = sp->sattr[SA_REMOTE_ADDR];

It is precisely because we reserve the space to store the built suckaddr
that there won't be a malloc() call made behind our back.

For some reason, it only complained about one call site.

Inspired by: CHERI