igb(4): Remove disconnected SYSCTL

The global hw.igb.rx_process_limit knob never was adhered to by the
in-tree version of this driver but similar functionality is available
via the device-specific dev.igb.N.iflib.rx_budget.

While at it, remove the - besides initialization of tx_process_limit -
unused {r,t}x_process_limit members.

(cherry picked from commit f221d35be7a5749e2a1246c81adc9c03c1dc545c)

share/man/man4/igc.4

@@ -3,7 +3,7 @@
 .\" Copyright 2021 Rubicon Communications, LLC (Netgate)
 .\" SPDX-License-Identifier: BSD-3-Clause
 .\"
-.Dd May 10, 2021
+.Dd January 9, 2023
 .Dt IGC 4
 .Os
 .Sh NAME
@@ -119,10 +119,6 @@ maximum delay in which a transmit interrupt is generated.
 .It Va hw.igc.sbp
 Show bad packets when in promiscuous mode.
 Default is false.
-.It Va hw.igc.rx_process_limit
-Maximum number of received packets to process at a time.
-Default is 100.
-A value of -1 means unlimited.
 .It Va hw.igc.eee_setting
 Disable or enable Energy Efficient Ethernet.
 Default 1 (disabled).

sys/dev/igc/if_igc.c

@@ -255,13 +255,6 @@ static int igc_debug_sbp = true;
 SYSCTL_INT(_hw_igc, OID_AUTO, sbp, CTLFLAG_RDTUN, &igc_debug_sbp, 0,
     "Show bad packets in promiscuous mode");
 
-/* How many packets rxeof tries to clean at a time */
-static int igc_rx_process_limit = 100;
-SYSCTL_INT(_hw_igc, OID_AUTO, rx_process_limit, CTLFLAG_RDTUN,
-    &igc_rx_process_limit, 0,
-    "Maximum number of received packets to process "
-    "at a time, -1 means unlimited");
-
 /* Energy efficient ethernet - default to OFF */
 static int igc_eee_setting = 1;
 SYSCTL_INT(_hw_igc, OID_AUTO, eee_setting, CTLFLAG_RDTUN, &igc_eee_setting, 0,
@@ -467,8 +460,6 @@ igc_if_attach_pre(if_ctx_t ctx)
 	adapter->media = iflib_get_media(ctx);
 	hw = &adapter->hw;
 
-	adapter->tx_process_limit = scctx->isc_ntxd[0];
-
 	/* SYSCTL stuff */
 	SYSCTL_ADD_PROC(device_get_sysctl_ctx(dev),
 	    SYSCTL_CHILDREN(device_get_sysctl_tree(dev)),

sys/dev/igc/if_igc.h

@@ -372,8 +372,6 @@ struct igc_adapter {
 
         u32		txd_cmd;
 
-        u32             tx_process_limit;
-        u32             rx_process_limit;
 	u32		rx_mbuf_sz;
 
 	/* Management and WOL features */