ppp_generic: Help GCC see that 'flen' is always initialized.

It's too stupid to see that we always set flen to something
before we use it in ppp_mp_explode():

drivers/net/ppp_generic.c: In function 'ppp_push':
drivers/net/ppp_generic.c:1314: warning: 'flen' may be used uninitialized in this function
drivers/net/ppp_generic.c:1314: note: 'flen' was declared here

This started warning after commit a53a8b56
("ppp: fix lost fragments in ppp_mp_explode() (resubmit)")

So just put an explicit unconditional initialization there to
hush it up.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp_generic.c

@@ -1431,6 +1431,7 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
 		*otherwise divide it according to the speed
 		*of the channel we are going to transmit on
 		*/
+		flen = len;
 		if (nfree > 0) {
 			if (pch->speed == 0) {
 				flen = totlen/nfree	;