How to get diff to report summary of new, changed and deleted lines

I think you are looking for diffstat. Simply pipe the output of diff -u to diffstat and you should get something like this.

 include/net/bluetooth/l2cap.h |    6 ++++++
 net/bluetooth/l2cap.c         |   18 +++++++++---------
 2 files changed, 15 insertions(+), 9 deletions(-)