Reserve space for the L2 header in BPF injected frames

[Mike Belopuhov]

Hi,

This reserves max_linkhdr bytes for a link layer header in the newly
allocated cluster in the bpf injection path like it's done for the
packets originating on the host itself (cf. tcp_output).  Saves us
time doing costly pool allocations later on.

I believe this has been tested by Yasuoka-san.

OK?

diff --git sys/net/bpf.c sys/net/bpf.c
index 86f5f6d..6cdf789 100644
--- sys/net/bpf.c
+++ sys/net/bpf.c
@@ -200,17 +200,18 @@ bpf_movein(struct uio *uio, u_int linktype, struct mbuf 
**mp,
 
        MGETHDR(m, M_WAIT, MT_DATA);
        m->m_pkthdr.ph_ifidx = 0;
        m->m_pkthdr.len = len - hlen;
 
-       if (len > MHLEN) {
-               MCLGETI(m, M_WAIT, NULL, len);
+       if (len + max_linkhdr > MHLEN) {
+               MCLGETI(m, M_WAIT, NULL, len + max_linkhdr);
                if ((m->m_flags & M_EXT) == 0) {
                        error = ENOBUFS;
                        goto bad;
                }
        }
+       m->m_data += max_linkhdr;
        m->m_len = len;
        *mp = m;
 
        error = uiomovei(mtod(m, caddr_t), len, uio);
        if (error)