test: use skip_if_platform_not_linux helper where possible

Rather than re-implementing these checks, we can use this test
framework's helper (introduced in commit
c934087b62, PR #24358) called in a test's
`skip_test_if_missing_module` method instead.

test/functional/feature_bind_extra.py

@@ -7,15 +7,12 @@ Test starting bitcoind with -bind and/or -bind=...=onion and confirm
 that bind happens on the expected ports.
 """
 
-import sys
-
 from test_framework.netutil import (
     addr_to_hex,
     get_bind_addrs,
 )
 from test_framework.test_framework import (
     BitcoinTestFramework,
-    SkipTest,
 )
 from test_framework.util import (
     assert_equal,
@@ -32,12 +29,11 @@ class BindExtraTest(BitcoinTestFramework):
         self.bind_to_localhost_only = False
         self.num_nodes = 2
 
-    def setup_network(self):
+    def skip_test_if_missing_module(self):
         # Due to OS-specific network stats queries, we only run on Linux.
-        self.log.info("Checking for Linux")
-        if not sys.platform.startswith('linux'):
-            raise SkipTest("This test can only be run on Linux.")
+        self.skip_if_platform_not_linux()
 
+    def setup_network(self):
         loopback_ipv4 = addr_to_hex("127.0.0.1")
 
         # Start custom ports by reusing unused p2p ports

test/functional/rpc_bind.py

@@ -4,8 +4,6 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test running bitcoind with the -rpcbind and -rpcallowip options."""
 
-import sys
-
 from test_framework.netutil import all_interfaces, addr_to_hex, get_bind_addrs, test_ipv6_local
 from test_framework.test_framework import BitcoinTestFramework, SkipTest
 from test_framework.util import assert_equal, assert_raises_rpc_error, get_rpc_proxy, rpc_port, rpc_url
@@ -17,6 +15,10 @@ class RPCBindTest(BitcoinTestFramework):
         self.num_nodes = 1
         self.supports_cli = False
 
+    def skip_test_if_missing_module(self):
+        # due to OS-specific network stats queries, this test works only on Linux
+        self.skip_if_platform_not_linux()
+
     def setup_network(self):
         self.add_nodes(self.num_nodes, None)
 
@@ -61,14 +63,9 @@ class RPCBindTest(BitcoinTestFramework):
         self.stop_nodes()
 
     def run_test(self):
-        # due to OS-specific network stats queries, this test works only on Linux
         if sum([self.options.run_ipv4, self.options.run_ipv6, self.options.run_nonloopback]) > 1:
             raise AssertionError("Only one of --ipv4, --ipv6 and --nonloopback can be set")
 
-        self.log.info("Check for linux")
-        if not sys.platform.startswith('linux'):
-            raise SkipTest("This test can only be run on linux.")
-
         self.log.info("Check for ipv6")
         have_ipv6 = test_ipv6_local()
         if not have_ipv6 and not (self.options.run_ipv4 or self.options.run_nonloopback):