Fix adb forward --list when forwarding a lot

The list action had some problems with large numbers of forwards:
 * adb_query() limited replies to 1024 B (and the print was useless)
 * the reply header's length could overflow (also in other commands)
 * ...and the client had no way of detecting it
 * writex() didn't retry on EAGAIN ("Resource temporarily unavailable")

This patch makes all "OKAY%04x" replies use a common function which
checks the length and limits it to 0xffff. This means that the client
can easily check for truncated replies.

Before: forward --list starts failing at 15-30 forwards (depending on
device serial and forward spec lengths).

After: no problems with forward --list.

Change-Id: Ie1e82c4d622f5c56e51abb26533ba17d40459914
adbd: Don't close/reopen FFS ep0 on disconnect

In case of bulk read/write failure or disconnect, transport_usb
calls usb_ffs_kick in order to force the daemon to re-open the
FunctionFS ep files as a way to soft restart the kernel driver.

However, there's no reason to always close the ep0 file, as it
would need to be reopened and the descriptors rewritten--this
is unnecessary, especially in the simple/frequent case of cable
disconnect, and causes the kernel driver to unbind and bind *all*
of the function drivers. This is causing USB Chapter 9 tests to fail.

Thus, try to reuse the same ep0 file handle across reconnects. In
case there is a failure, the ep1/ep2 opens would fail and all the
file handles get dropped. For the adb root case, the entire daemon
gets restarted anyway.

Change-Id: I0840085c52a0795dcb2d751c39aa4a436c039ee2
adb: fix windows build after "forward --list" fix.

EWOULDBLOCK is not there on windows.
It gets translated by the adb_write() wrapper into EGAIN.
But the Linux one does not translate EWOULDBLOCK into EGAIN.
Without EWOULDBLOCK, it works just fine.

Change-Id: Ic293be392aa4364637428ea94ef87890ffa09b9b
Signed-off-by: JP Abgrall <jpa@google.com>