MFC r229694:

MFC r229694:

r222004 changed sbuf_finish() to not clear the buffer error status. As a
consequence sbuf_len() will return -1 for buffers which had the error
status set prior to sbuf_finish() call. This causes a problem in
pfs_read() which purposely uses a fixed size sbuf to discard bytes which
are not needed to fulfill the read request.

Work around the problem by using the full buffer length when
sbuf_finish() indicates an overflow. An overflowed sbuf with fixed size
is always full.

PR:		kern/163076

git-svn-id: svn://svn.freebsd.org/base/stable/9@230485 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f