panic in `Snmp::from_buf_read` due to missing IcmpMsg line

[eminence]

---- net::tests::test_snmp stdout ----
thread 'net::tests::test_snmp' panicked at /home/achin/devel/procfs/procfs-core/src/net.rs:1038:41:
called `Option::unwrap()` on a `None` value

This is because our parser expects (but ignores) a line that starts with IcmpMsg but this is sometimes missing on my 6.8.9 kernel:

Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests OutDiscards OutNoRoutes ReasmTimeout ReasmReqds ReasmOKs ReasmFails FragOKs FragFails FragCreates OutTransmits
Ip: 2 64 12063 0 1 0 0 0 11952 8953 0 0 0 0 0 0 0 0 0 8953
Icmp: InMsgs InErrors InCsumErrors InDestUnreachs InTimeExcds InParmProbs InSrcQuenchs InRedirects InEchos InEchoReps InTimestamps InTimestampReps InAddrMasks InAddrMaskReps OutMsgs OutErrors OutRateLimitGlobal OutRateLimitHost OutDestUnreachs OutTimeExcds OutParmProbs OutSrcQuenchs OutRedirects OutEchos OutEchoReps OutTimestamps OutTimestampReps OutAddrMasks OutAddrMaskReps
Icmp: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Tcp: RtoAlgorithm RtoMin RtoMax MaxConn ActiveOpens PassiveOpens AttemptFails EstabResets CurrEstab InSegs OutSegs RetransSegs InErrs OutRsts InCsumErrors
Tcp: 1 200 120000 -1 177 14 0 6 4 11155 10083 18 0 94 0
Udp: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti MemErrors
Udp: 2772 0 0 1890 0 0 0 745 0
UdpLite: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti MemErrors
UdpLite: 0 0 0 0 0 0 0 0 0