init.qcom.usb.sh: Initialize persist.sys.usb.config.extra property

commit c6a666ce "init.qcom.usb.sh: Remove the diag_extra section"
removed the section that sanitizes the persist.sys.usb.config.extra
property. However, if it is unset, the init.qcom.usb.rc rules will
fail to parse the empty property upon USB composition switch to
RNDIS. Instead, it needs to at least be initialized to 'none' if
not already set.

Change-Id: I98c08180bcbe791667d0ccb866a11796a7debc12
init.qcom.sh/rc: Set tx qmult to 2 to avoid trb overflow

number of trbs availabel to controller are 1024. u_ether driver
allocates 200 requests when tx_qmult is 5. When aggregation
enabled, each request can have 10 trbs. In worst case scenario, there
there can be flooded with 2000 trbs. To avoid such scenarios, use
tx_qmult value 2.

Change-Id: Ia63807ab0d0018add089555b7ef0b68ddbc8dda8
(cherry picked from commit 692c030f15ae357a5e81a5944cf176c533ceec35)
Merge "init.qcom.sh/rc: Set tx qmult to 2 to avoid trb overflow"
Merge "init.qcom.usb.sh: Initialize persist.sys.usb.config.extra property"