soc: silabs: siwg917: Restore missing config and update default settings

Commit `2844850d` inadvertently omitted
`SL_SI91X_CUSTOM_FEAT_SOC_CLK_CONFIG_160MHZ`. This commit restores
the missing flag to ensure proper SOC clock setup.

Additionally, `SL_SI91X_CUSTOM_FEAT_LIMIT_PACKETS_PER_STA` is now enabled
as the default setting, aligning with the driver Kconfig.

Signed-off-by: Arunmani Alagarsamy <arunmani.a@silabs.com>