le_audio: lowering the value of ISO suspend time

Currently set up value of 5 second seems to be no longer valid value for
suspending ISO channels. This helps also speeds up unicast->broadcast
handover switch.

Tag: #bug
Bug: 349311566
Flag: Exempt, minor timeout change
Test: atest bluetooth_le_audio_test
Change-Id: Ie0628e79ba159c12f0402d22fd2050bc13786662