Update TCP buffer size for 5G data connections

In 5G NSA, the TCP buffer size is not updated when the data connection
is established because the RAT type of the data connection is LTE.
Framework knows the 5G data conenctions when the there is a 5G physical
channel reported, so we need to update the tcp buffer size at that
moment.

Bug: 135941346
Test: atest ServiceStateTrackerTest
Merged-In: Id545e007b191e0b28aaa5c976484bb27259679fe
Change-Id: Id545e007b191e0b28aaa5c976484bb27259679fe