Signed-off-by: Robert Marshall KI4MCW <ki4mcw@gmail.com>

According to the protocol document...

http://www.tapr.org/pdf/AX25.2.2.pdf

...bits 6 and 5 in the SSID should be set to 1 if unused. In a
simplified use case such as APRS, bit 7 can be set to 0 for the source
and destination SSIDs. This yields an offset of 0x60 for all SSIDs in
the path, which can be ORed in prior to transmission.

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4618 38d2e660-2303-0410-9eaa-f027e97ec537