net/tap: fix eBPF file descriptors leakage

net/tap: fix eBPF file descriptors leakage

When a user creates an RSS rule, the tap PMD dynamically allocates
a 'flow' data structure, and uploads BPF programs (represented by file
descriptors) to the kernel.
The kernel might reject the rule (due to filters overlap, for example)
in which case, flow memory should be freed and BPF file descriptors
should be closed.
In the corrupted code there were scenarios where BPF file descriptors
were not closed.
The fix is to add a new function - tap_flow_free(), which will make sure
to always close BPF file descriptors before freeing the flow allocated
memory.

Fixes: 036d721a8229 ("net/tap: implement RSS using eBPF")

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Pascal Mazon <pascal.mazon@6wind.com>