MemcacheCommand: handle TCP options in packet parsing.
MemcacheCommand: handle TCP options in packet parsing.

The data offset field of a TCP header contains the number of words the
header is long (minimum 5).  Previously, this code assumed all TCP
headers were exactly 5 words long and would treat the TCP options as
payload. This patch makes the parser respect the data offset field and
start parsing data at the correct point.

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