In sbappend*() family of functions clear M_PROTO flags of incoming
mbufs. sbappendstream() already does this in m_demote().

PR:		196174
Sponsored by:	Nginx, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276058 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f