GCS_MAVLink: add option to forward messages with bad CRCs

[peterbarker]

[tridge]

approved in principle, needs to build though :-)

[peterbarker]

Board                    AP_Periph  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
CubeOrange-periph-heavy  112                                                                   
Durandal                            104    *           112     112               120    112    104
Hitec-Airspeed           *                                                                     
KakuteH7-bdshot                     104    *           112     112               104    104    104
MatekF405                           80     *           88      80                80     88     88
Pixhawk1-1M-bdshot                  80                 80      88                80     88     80
f103-QiotekPeriph        *                                                                     
f303-Universal           *                                                                     
iomcu                                                                *                         
revo-mini                           80     *           80      80                80     88     88
skyviper-v2450                                         96                                      

[peterbarker]

Added DevCallEU here to discuss adding two bits rather than one as @nexton-winjeel suggested.

[peterbarker]

From Discord #mavlink

[2:08 AM]Fenix: @Peter Barker 
I tested a custom build based on PR 25419 branch.

With the MAV{X}_OPTIONS parameter bit FORWARD_BAD_CRC (value 8) set,
my setup — Computer → USB → FC → Serial → Companion Computer — successfully routes both custom MAVLink messages and commands.

Everything works as intended, so I’d suggest merging this PR.
[8:48 AM]Peter Barker: Thanks, I'll try to move that forward in the next week or so

[peterbarker]

Board,blimp,bootloader,copter,heli,plane,rover,sub
CubeOrange,112,*,104,104,112,104,104