Greg noted in the pull request, "Lots of little things here, over 1600 patches or so. [Notable] is all of the good Lustre work happening, those developers have finally woken up and are cleaning up their code greatly. The Outreachy intern application process is also happening, which brought in another 400 or so patches. Full details are in the very long shortlog."
So it looks like almost a quarter of the patches are from Outreachy, the group providing paid internships for women and other "underrepresented groups in tech" to work on the Linux kernel and related open-source projects. As outlined recently, the Outreachy 2016 summer deadline is fast approaching. This round the program is open "internationally to women (cis and trans), trans men, and genderqueer people. Additionally, they are open to residents and nationals of the United States of any gender who are Black/African American, Hispanic/Latin@, American Indian, Alaska Native, Native Hawaiian, or Pacific Islander." A list of the Linux kernel Outreachy potential projects can be found via this KernelNewbies.org Wiki page.
Besides the Lustre churn, there are also many updates for Octeon, WILC1000, RTL8188EU, RTL8192U, RTL8723AU, WLAN-NG, and various Android code. In the end the staging updates for Linux 4.6 add 45k new lines of code while removing 50k lines of code.