rmnet_ctl: re-arrange ipa registration

Re-arrange ipa registration sequence to handle cases where rmnet_ctl
is being initialized before ipa is ready.

Change-Id: Ic8416ad8f96f818e32f1320e997287ebfe755d03
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>