Bluetooth: RFCOMM: pull credit byte with skb_pull_data()

Bluetooth: RFCOMM: pull credit byte with skb_pull_data()

rfcomm_recv_data() treats the first payload byte as a credit field when
the UIH frame carries PF and credit-based flow control is enabled.

After the header has been stripped, the PF/CFC path consumes that byte
with a direct skb->data dereference followed by skb_pull(). A malformed
short frame can reach this path without a byte available.

Use skb_pull_data() so the length check and pull happen together before
the returned credit byte is consumed.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>