SdpManager: Use class variable and not static one

This is addressing an errorProne warning: StaticAssignmentInConstructor
Since SdpManager only live within it's intanciation. It doesn't require
setting a static variable

Bug: 323672160
Test: atest BluetoothInstrumentationTests
Change-Id: Ib2f1d83e58ebd6938afc1ff33091faa2c85ee433