packet lib: don't crash with bogus ospf packet

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofctl_v1_2/3: Fully support the match combinations for VLAN ID

Currently, when VLAN ID match field is specified,
ofctl_v1_[23] is compatible with only match combination 1) of
the following three match combinations.
This patch makes it possible to set the all three combinations.

  Match combinations for VLAN ID :
    1) To match only packets with VLAN tag and VID equal value
    2) To match only packets without a VLAN tag
    3) To match only packets with a VLAN tag regardless of its value

In order to set the match combinations 2) or 3), please describe
"dl_vlan" field as hexadecimal string value like as follows.

  Before applying this patch:
    {"dl_vlan": 3 }              # int

  After applying this patch:
    {"dl_vlan": 3 }              # int (same as before applying)
    {"dl_vlan": "0x0000"}        # hexadecimal string without mask
    {"dl_vlan": "0x1000/0x1000"} # hexadecimal string with mask

NOTE: When "dl_vlan" field is described as decimal int value,
      OFPVID_PRESENT(0x1000) bit is automatically applied.
      OTOH, OFPVID_PRESENT(0x1000) bit is NOT automatically applied
      to hexadecimal string value.

For curl command examples, please refer to the following page in Ryu-documentation.
http://ryu.readthedocs.org/en/latest/app/ofctl_rest.html#example-of-vlan-id-match-field

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
doc/app/ofctl_rest: Add command examples for OFPVID_NONE/PRESENT

Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>