net: skbuff: fix compile error in skb_panic()

I get the following build error on next-20130213 due to the following
commit:

commit f05de73b ("skbuff: create
skb_panic() function and its wrappers").

It adds an argument called panic to a function that uses the BUG() macro
which tries to call panic, but the argument masks the panic() function
declaration, resulting in the following error (gcc 4.2.4):

net/core/skbuff.c In function 'skb_panic':
net/core/skbuff.c +126 : error: called object 'panic' is not a function

This is fixed by renaming the argument to msg.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Jean Sacren <sakiwit@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>