[NETFILTER]: Fix warnings in ip_nat_snmp_basic.c

[NETFILTER]: Fix warnings in ip_nat_snmp_basic.c

net/ipv4/netfilter/ip_nat_snmp_basic.c: In function 'asn1_header_decode':
net/ipv4/netfilter/ip_nat_snmp_basic.c:248: warning: 'len' may be used uninitialized in this function
net/ipv4/netfilter/ip_nat_snmp_basic.c:248: warning: 'def' may be used uninitialized in this function
net/ipv4/netfilter/ip_nat_snmp_basic.c: In function 'snmp_translate':
net/ipv4/netfilter/ip_nat_snmp_basic.c:672: warning: 'l' may be used uninitialized in this function
net/ipv4/netfilter/ip_nat_snmp_basic.c:668: warning: 'type' may be used uninitialized in this function

Signed-off-by: David S. Miller <davem@davemloft.net>