lib: relicense smb_strtoul(l) under LGPLv3

Quoting Andrew on samba-technical:

We just noticed this because debian failed to build due to an extra symbol added to our internal samba-util library.

samba-util is a 'big ball of mud' library of Samba stuff, licensed GPLv3 and very, very helpful for stuff in Samba. Work is slowly happening to try and pry it apart into a directed graph of smaller libraries, but for now that is how it works.

Either way, it is GPLv3 and is therefore not permitted to be a dependency of libwbclient, which is our tiny winbind client lib for linking into OTHER PARTS of a running system, eg nss, pam and potentially other tools. It is LGPLv3, and important distinction.

I don't know why our ABI stuff didn't pick it up, but I know some on the team have ideas about how to reinforce that.

We need to disconnect these two parts, then try and undo the damage in the distributions due to the extra symbols.

This MR tries to address this.

Sven, are you ok with the relicensing of your code?