gdb_server: Do not set gdb_con->sync to true for new connections

gdb_server: Do not set gdb_con->sync to true for new connections

In GDB connected to OpenOCD there is a command "monitor gdb_sync" which makes
next stepi command to be ignored while GDB still will get an updated target
state. This command sets gdb_connection->sync field to true to notify that stepi
should be ignored. This field is set to true for all new connection and is set
to false after first "continue" command. However if first resume command is
stepi/nexti then it will be ignored and result will confuse GDB client, it will
report that target received signal SIGINT. This patch sets this field to false
for new connections, thus stepi/nexti will work properly when it is a first
resume command.

Change-Id: I7c9ebd69c3dc35f3e316041aa99f4e9d3425c0b6
Signed-off-by: Anton Kolesov <akolesov@synopsys.com>
Reviewed-on: http://openocd.zylin.com/1587
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>