Rework the Group's Socket Option Handling Facilities

[maxsharabayko]

The design of the socket option handling of a group is a bit fragile with respect to data types.
The data type (optlen) returned by the API call (srt_getopt) may not match the type of the variable that stores the value.
SRTO_PBKEYLEN, SRTO_PAYLOADSIZE and SRTO_CONNTIMEO store values in a variable of a different type compared to the one coming from the API (See PR #3066). Hence the importOption function with its call to getOptDefault to get optlen and value is not error-prone.

It would be better to at least use a certain type assigned to a specific option (int32_t, int64_t, bool, char*).

This way the importOption can be improved and take the assigned static type to the option symbol instead of relying on the field's type.