fix(dracut.sh): use gawk for strtonum

[thesamesam]

This pull request changes dracut.sh and dracut-functions.sh to use gawk instead of awk because we're using strtonum.

strtonum is a gawkism and is not available in all awks, e.g. mawk. Use gawk to avoid failure.

Fixes: f32e95bcadbc5158843530407adc1e7b700561b1

Changes

Checklist

• [X] I have tested it locally
• [X] I have reviewed and updated any documentation if relevant
• [N/A] I am providing new code and test(s) for it

Fixes #

[thesamesam]

cc @keentux

[LaszloGombos]

Thanks @thesamesam .

Make sense to me to land this as is, but I hope to improve it even further and support mawk by carrying our own strtonum implementation.