qemu-vmsr-helper: fix socket loop breakage

qemu-vmsr-helper: fix socket loop breakage

Between v5 and v6 of the series, the socket loop of qemu-vmsr-helper was changed to
allow sending multiple requests on the same socket.  Unfortunately, the condition
of the while loop is botched and the loop will never be entered.  Clean it up, and
also unify the handling of error reporting.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>