Increase MAX_MSS to 32K

[nshopik]

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• Brief description of code changes (suitable for use as a commit message):

Today hardware capable 16K MTU already, this raise MAX_MSS to 32K which can be set via -M option.

I would increased to max allowed for ipv4 datagram size 65536 - 20 - 20, but its not possible to set value above 32767 manually as it return error.
setsockopt(3, SOL_TCP, TCP_MAXSEG, [32768], 4) = -1 EINVAL (Invalid argument)