allow large bpf writes

[David Gwynne]

now that we have large clusters, we can easily support packets up to 64k in 
length.

is there doco i have to update?

ok?

Index: bpf.c
===================================================================
RCS file: /cvs/src/sys/net/bpf.c,v
retrieving revision 1.103
diff -u -p -r1.103 bpf.c
--- bpf.c       12 Jul 2014 18:44:22 -0000      1.103
+++ bpf.c       18 Sep 2014 09:38:56 -0000
@@ -172,7 +172,7 @@ bpf_movein(struct uio *uio, u_int linkty
                return (EIO);
        }
 
-       if (uio->uio_resid > MCLBYTES)
+       if (uio->uio_resid > MAXMCLBYTES)
                return (EIO);
        len = uio->uio_resid;
 
@@ -181,7 +181,7 @@ bpf_movein(struct uio *uio, u_int linkty
        m->m_pkthdr.len = len - hlen;
 
        if (len > MHLEN) {
-               MCLGET(m, M_WAIT);
+               MCLGETI(m, len, NULL, M_WAIT);
                if ((m->m_flags & M_EXT) == 0) {
                        error = ENOBUFS;
                        goto bad;