install-dependencies.sh: add diffutils
install-dependencies.sh: add diffutils

The dpdk build system needs cmp to check its caches. This is supplies
by diffutils, so add it to the dependencies.
Message-Id: <5ef6fdf1bf907adf2349ce2309bf3e8f6e930159@scylladb.com>

dreamsxin/seastar,scylladb/seastar,avikivity/seastar,dreamsxin/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,cloudius-systems/seastar,cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,dreamsxin/seastar