Bug#1066721: netcat: FTBFS: netcat.c:1557:9: error: implicit declaration of function ‘helpme’ [-Werror=implicit-function-declaration]

[Andreas Beckmann]

Followup-For: Bug #1066721
Control: tag -1 patch

I've committed a fix to the git repository. Will followup with a NMU in a
few days. I've also enabled the salsa-ci pipeline for the package.

Andreas