[CIPSO]: remove duplicated code in the cipso_v4_*_getattr() functions

The bulk of the CIPSO option parsing/processing in the cipso_v4_sock_getattr()
and cipso_v4_skb_getattr() functions are identical, the only real difference
being where the functions obtain the CIPSO option itself.  This patch creates
a new function, cipso_v4_getattr(), which contains the common CIPSO option
parsing/processing code and modifies the existing functions to call this new
helper function.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>