Change DHCP inline function definition to static inline

Compiling Pi-hole FTL w/o optimization (release type "DEBUG") results in
the following error during linking:

'''
x86_64-buildroot-linux-uclibc/bin/ld: tools/CMakeFiles/tools.dir/dhcp-discover.c.o: in function `create_dhcp_socket':
/home/data/buildroot.experimental/build/pihole-ftl-6.6/src/tools/dhcp-discover.c:88:(.text+0xac): undefined reference to `start_lock'
x86_64-buildroot-linux-uclibc/bin/ld: /home/data/buildroot.experimental/build/pihole-ftl-6.6/src/tools/dhcp-discover.c:90:(.text+0xe9): undefined reference to `end_lock'
[...]
x86_64-buildroot-linux-uclibc/bin/ld: tools/CMakeFiles/tools.dir/dhcpv6-discover.c.o: in function `recv_adv':
/home/data/buildroot.experimental/build/pihole-ftl-6.6/src/tools/dhcpv6-discover.c:706:(.text+0x137f): undefined reference to `start_lock'
x86_64-buildroot-linux-uclibc/bin/ld: /home/data/buildroot.experimental/build/pihole-ftl-6.6/src/tools/dhcpv6-discover.c:709:(.text+0x13b1): undefined reference to `end_lock'
[...]
'''

When generating code without optimization, gcc ignores the inline
directive. Code for this function is generated once, but not marked
as global (because the extern keyword is missing), which results
in the observed linker error for all other compilation units.

Change the function definition to static inline, which will force the
compiler to include a static copy of the function in every compilation
unit, if the function is not inlined.

Signed-off-by: Andreas Ziegler <[email protected]>

Author: aeolio

src/tools/dhcp-discover.h

@@ -20,12 +20,12 @@ int get_hardware_address(const int sock, const char *iname, unsigned char *mac);
 // Global lock used by all threads
 extern pthread_mutex_t dhcp_lock;
 
-inline void start_lock(void)
+static inline void start_lock(void)
 {
 	pthread_mutex_lock(&dhcp_lock);
 }
 
-inline void end_lock(void)
+static inline void end_lock(void)
 {
 	pthread_mutex_unlock(&dhcp_lock);
 }