Documentation: net/smc: correct old value of smcr_max_recv_wr

The smc-sysctl.rst documentation incorrectly stated that
the previous hardcoded maximum number of WR buffers on
the receive path (smcr_max_recv_wr) was 16.
The correct historical value used before the introduction of
the sysctl control was 48. Update the documentation to reflect
the accurate historical value. Also fix a couple of minor typos.

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Signed-off-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Link: https://patch.msgid.link/20260424052336.3262350-1-mjambigi@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>