wifi: simplelink: implement 'is_supported' socket offload cb

Check if requested socket family, type and protocol are all supported by
the driver, instead of blindly acknowledging every possible variant.

Reuse switch statements checking valid parameter values that were
already part of simplelink_socket() function, by creating 3 helper
functions for conversion of each parameter (family, type and protocol)
from Zephyr to Simplelink values.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>