Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

make sure that socket's send and receive buffers are properly sized

Submitted by: Iain Hibbert plunky at rya-online dot net
MFC after: 3 weeks

Add btpand(8) daemon from NetBSD. This daemon provides support for
Bluetooth Network Access Point (NAP), Group Ad-hoc Network (GN) and
Personal Area Network User (PANU) profiles.

Obtained from: NetBSD
MFC after: 1 month