Bluetooth: controller: Fix redundant length update event

Fix generation of redundant length update event when no
change in effective octets or time.

Fixes LL.TS.5.0.2 conformance tests:
LL/CON/MAS/BV-73-C [Master Data Length Update - Responding
                    to Data Length Update Procedure; LE 1M
                    PHY]
LL/CON/MAS/BV-74-C [Master Data Length Update - Initiating
                    Data Length Update Procedure; LE 1M PHY]
LL/CON/MAS/BV-76-C [Master Data Length Update - Responding
                    to Data Length Update Procedure; LE 2M
                    PHY]
LL/CON/MAS/BV-77-C [Master Data Length Update - Initiating
                    Data Length Update Procedure; LE 2M PHY]
LL/CON/SLA/BV-77-C [Slave Data Length Update - Responding
                    to Data Length Update Procedure; LE 1M
                    PHY]
LL/CON/SLA/BV-78-C [Slave Data Length Update - Initiating
                    Data Length Update Procedure; LE 1M PHY]
LL/CON/SLA/BV-80-C [Slave Data Length Update - Responding
                    to Data Length Update Procedure; LE 2M
                    PHY]
LL/CON/SLA/BV-81-C [Slave Data Length Update - Initiating
                    Data Length Update Procedure; LE 2M PHY]

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>