Sanitize invalid TCP_KEEPINTVL and simplify TCP_KEEPALIVE_ABORT_THRESHOLD on Solaris

[panjf2000]

Two things:

1. Avoid invalid value being set to TCP_KEEPINTVL and raising an error
2. Simplify setting TCP_KEEPALIVE_ABORT_THRESHOLD by eliminating the needless calculations

The time between each consequent probes is set by TCP_KEEPINTVL in seconds. The minimum value is ten seconds. The maximum is ten days, while the default is two hours.

From TCP on Solaris

[panjf2000]

Ping @oranagra

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