Floss: Use SOCK_STREAM for L2CAP socket

Previously we uses SOCK_SEQPACKET but there is no clear advantage
of using it. Additionally we use SOCK_STREAM everywhere else.
This CL makes Floss uses SOCK_STREAM.

Bug: 271828292
Test: Pass CTSV BLE CoC Client Test
Change-Id: I8d9beaf7800477d356be9b8bedf8959c412e731b