Config.uk: Add dependencies for POSIX libraries

Config.uk: Add dependencies for POSIX libraries

Release 0.10 added `posix-socket` and `posix-event` internal libraries
to the Unikraft core. Consequently, libraries depending on networking
functionality need to be updated to include `posix-socket` and
`posix-event`.

This commit adds `LIBPOSIX_SOCKET` and `LIBPOSIX_EVENT` dependency to
`Config.uk`.

Signed-off-by: Razvan Deaconescu <razvan.deaconescu@cs.pub.ro>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Approved-by: Alexander Jung <alex@unikraft.org>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Pull-Request-Closes: #6