Fixes net.ifinfo failure

[vsky279]

Fixes #3249.

• This PR is for the dev branch rather than for master.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/*.

This seems to be an easy catch. Only 0 or 1 are eligible parameters to eagle_lwip_getif and dhcp table can be added to the resulting table only when dhcp table is created.

[nwf]

Looks right to me. @vsky279 Can I get you to squash the two commits together yourself so we can do the "rebase and merge" rather than "squash and merge" that will, I think, leave my name on it rather than yours and @marcelstoer's?

[marcelstoer]

that will, I think, leave my name on it

Hhmm, what makes you think so? Git(Hub) just records the committer separately from the author if you "squash and merge": https://github.com/nodemcu/nodemcu-firmware/commits/dev. Looks all dandy to me.

[vsky279]

It's squashed now :-)

[marcelstoer]

All my tests passed.