gdb_server: fix a comment in gdb_new_connection()

gdb_server: fix a comment in gdb_new_connection()

On 2008-03-05, before git's age, commit 6d9501467441 adds a
comment about unobserved ACK supposedly sent by GDB at connection.

The ACK is sent since GDB 3.95 (1999-05-04), but a bug introduced
in GDB 6.5 (2006-06-21) and fixed in GDB 7.0 (2009-10-06) makes
GDB sending the query for "supported packets" before sending the
ACK. Due to the bug, the author of the commit failed to see the
ACK.

Change-Id: I574a8013e7d159d1c71087af83b7c2ce92be86bd
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6769
Tested-by: jenkins