dfc: not caching grant for removed bearers

If a grant indication for a bearer has "removed" flag set, caching
the bearer could lead to data stall for the next data call because
modem will not send grant for this bearer during powersave.

Do not cache grant for the removed or disabled bearers. Also make sure
a bearer is flow enabled when it is associated with a tx queue.

Change-Id: I7eca597e3cc7d5a0bfe523201c454fb45e66a3a0
Signed-off-by: Weiyi Chen <quic_weiyic@quicinc.com>