Learn SG - correct matches for rules for ICMP and other general changes

1. When configuring an ICMP allow rule - I got this:
table=42, priority=61010,ip,metadata=0x30000000000/0x1fffff0000000000 actions=learn(table=252,idle_timeout=60,hard_timeout=60,priority=61010,cookie=0x6900000,eth_type=0x800,NXM_OF_IP_SRC[]=NXM_OF_IP_DST[],NXM_OF_IP_PROTO[],load:0x1->NXM_NX_REG6[0..7]),resubmit(,17)

We need to match on ICMP not IP in this case - otherwise it conflicts with other SG rules

2. Why dont we match on both directions of IP? This would be more correct - add NXM_OF_IP_DST[]=NXM_OF_IP_SRC[]