MFC 85d8d30f9f70:
Don't allow allocating a new send tag on an INP which is being torn down.
This fixes a potential send tag leak.

Approved by: re (gjb)
Reviewed by: rrs@
Sponsored by: Mellanox Technologies // NVIDIA Networking

(cherry picked from commit 85d8d30f9f7046f5e89295352ded49135b25fbe3)