plugin/ssa_extract.c: Fix pkeys extraction

Pkeys are extracted from pkey_tbl->new_blocks blocks
vector rather than from pkey_tbl->keys quick map.

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>
plugin/ssa_extract.c: Fix port_tbl_rec->pkey_tbl_offset units

pkey_tbl_offset resolution is changed to bytes instead
of pkey records (2 bytes).

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>
plugin/ssa_extract.c: Limit for the maximum number of pkeys supported per port

SSA port record 'pkey_tbl_size' field type is be16_t, therefore
maximum size of pkey records chunk is 64K and thus the maximum
number of pkey records supported per port is 32K.

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>