package/libnet: bump to version 1.2

package/libnet: bump to version 1.2

- As stated in https://sourceforge.net/projects/libnet-dev/, "this
  project no longer uses sourceforge", so switch site to
  https://github.com/libnet/libnet
- Drop patch (already in version)
- Use the new LICENSE file, same as previous but with updated copyright
  years:
  https://github.com/libnet/libnet/commit/e4fb7e9a1ac7b1695235519ac81bfda616776504
- Update indentation in hash file (two spaces)

https://github.com/libnet/libnet/releases/tag/v1.2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>