Handle G_IO_HUP in tcp_chr_read for tcp chardev

Since commit cdaa86a54b232572bba594bf87a7416e527e460c
("Add G_IO_HUP handler for socket chardev")
GLib limitation results in a bug on Windows host. Steps to reproduce:

Start qemu: qemu-system-i386 -qmp tcp:127.0.0.1:4444:server:nowait
Connect with telnet: telnet 127.0.0.1 4444
Try sending some data from telnet.
Expected result: answers from QEMU.
Observed result: no answers (actually tcp_chr_read is not called at all).

Due to GLib limitations it is not possible to create several watches on one
channel on Windows hosts. See bug #338943 in GNOME bugzilla for details:
https://bugzilla.gnome.org/show_bug.cgi?id=338943

This reimplements commit cdaa86a54b232572bba594bf87a7416e527e460c
("Add G_IO_HUP handler for socket chardev") using a single watch:

Handle G_IO_HUP in tcp_chr_read instead. It is already watched by a
corresponding watch.  Remove the second watch with its handler.

Cc: Antonios Motakis <a.motakis@virtualopensystems.com>
Cc: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Kirill Batuzov <batuzovk@ispras.ru>
Signed-off-by: Nikita Belov <zodiac@ispras.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
