usb: gadget: u_bam_data: get rid of bam rndis state

commit 3638bf12(u_bam_data: Fix issue with RNDIS adaptor
enable/disable) introduced rndis specific states to
handle rndis adaptor enable/disable. This can be done
by moving the endpoint tx/rx req related data structure
allocation and initialization to bam_data_connect() so
that it will be allocated when usb cable is connected.
When rndis adaptor is disabled directly queue disconnect
work. When adaptor is enabled back same data structures
are not allocated again. Also rename is_connected flag
to is_ipa_connected and use it to track ipa bam connect
and disconnect only.

CRs-Fixed: 773365
Change-Id: I8df586176a2052005615aefd6107a899d47b080f
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>