isotpsniffer: option for no quitting on invalid message received

[maziu]

Hello,

I was working with isotpsniffer, and found out that if invalid / incomplete / malformed iso tp message is received, isotpsniffer immediately quits:

┌──(kali㉿kali)-[~/can-utils]
└─$ ./isotpsniffer -s 1D9 -d 481 vcan0
read socket t: Invalid or incomplete multibyte or wide character
                                                                                                                    
┌──(kali㉿kali)-[~/can-utils]
└─$ 

This wasn't desired behaviour, as I had to use malformed frames for target debugging purposes

This PR address this issue and adds additional command line option (-q) to continue receiving if read command returns -1

./isotpsniffer -s 1D9 -d 481 -q vcan0
read socket s: Invalid or incomplete multibyte or wide character
read socket t: Invalid or incomplete multibyte or wide character
 vcan0  481  [6]  00 04 12 02 10 06  - '......'
 vcan0  1D9  [6]  00 04 22 02 12 00  - '.."...'
 vcan0  481  [16]  00 0E 12 0C 0A 0A 08 08 12 06 0A 04 52 BB 74 EF  - '............R.t.'
 vcan0  1D9  [14]  00 0C 22 0A 1A 08 12 06 0A 04 52 BB 74 EF  - '..".......R.t.'
^C
                                                                                                                    
┌──(kali㉿kali)-[~/can-utils] 

As side effect, when socket is closed while isotpsniffer is working, isotpsniffer will NOT exit - that's why this is added as option, not default behaviour:

$ ./isotpsniffer -s 1D9 -d 481 -q vcan0
read socket s: Invalid or incomplete multibyte or wide character
read socket t: Invalid or incomplete multibyte or wide character
 vcan0  481  [6]  00 04 12 02 10 06  - '......'
 vcan0  1D9  [6]  00 04 22 02 12 00  - '.."...'
read socket t: Network is down
[continues to work. do not quit]

I see possibility to make decision about exit basing on errno value. What do you think about that? Any comments appreciated.

[hartkopp]

Sorry for the mess in this review. It was the first time where I not only added single comments but used the "start a review" button ...

Thanks for the contribution!

[maziu]

Provided changes you requested - sorry that it took so long

[maziu]

Sorry for the force push. It was non-intentional change, I've modified github actions script on my fork and forgot that it will go also to this PR (facepalm). Force push reverted it to previous state