splitting m_flags to pkthdr.flags + m_flags

[Gleb Smirnoff]

  Hello networkers,

  some (most) of m_flags bits are describing features that can
be present on a packet only, not on a single mbuf. Since we are
close to exhaustion of available bits, and many subsystems prefer
to use one of M_PROTO bits instead of grabbing a flag, I propose
to split m_flags to two parts:

In the m_flags remain:
#define M_EXT           0x00000001 /* has associated external storage */
#define M_PKTHDR        0x00000002 /* start of record */
#define M_EOR           0x00000004 /* end of record */
#define M_RDONLY        0x00000008 /* associated data is marked read-only */
and all M_PROTO flags.

struct pkthdr grows by one word and its new flag word now
posesses:

#define M_BCAST         0x00000200 /* send/received as link-level broadcast */
#define M_MCAST         0x00000400 /* send/received as link-level multicast */
#define M_FRAG          0x00000800 /* packet is a fragment of a larger packet */
#define M_FIRSTFRAG     0x00001000 /* packet is first fragment */
#define M_LASTFRAG      0x00002000 /* packet is last fragment */
#define M_SKIP_FIREWALL 0x00004000 /* skip firewall processing */
#define M_VLANTAG       0x00010000 /* ether_vtag is valid */
#define M_PROMISC       0x00020000 /* packet was not for us */
#define M_FLOWID        0x00400000 /* deprecated: flowid is valid */
#define M_HASHTYPEBITS  0x0F000000 /* mask of bits holding flowid hash type */

Some M_PROTO abusements like M_FASTFWD_OURS and recently added M_IP_NEXTHOP
also go to the pkthdr mbuf flags.

P.S.
An attentive reader may have noticed that I missed M_NOFREE and M_FREELIST.
Yep, these flags coming from historical mbuf allocator from FreeBSD 4.x times
are about to be deleted, we carefully examine them, but never set. Patch
for review attached.

-- 
Totus tuus, Glebius.
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