hping: fix build against gcc-10 (-fno-common)

[trofi]

gcc-10 changed the default from -fcommon to fno-common: https://gcc.gnu.org/PR85678

As a result build fails as:

ld: scan.o:/build/hping/hping2.h:360: multiple definition of `delaytable'; main.o:/build/hping/hping2.h:360: first defined here

The change moves variable definitions to .c file.

[hackman]

This change worked for me. I was thinking of adding the same thing :) Thank you!